Add `updateTexture` & some shortcuts in Sprite; Cosmetic (#4000) ...

* Add `updateText` and some shortcuts for texture

* Add `updateText`.  If a sprite is create by a canvas ,  when the canvas's changed , user could call `updateText` for updating sprite.
* Add some shortcuts for accessing  some properties of sprite._texture.

* Cosmetic, for DRY

Just define some local vars for accessing properties of `this` , for DRY.

* remove the changing of Sprite

Fixed if statement checks that do not work if the stop point is set to 0 (#3948)

Measure Text API, expanded (#3921) ...

* Added TextStyle.measure function (Applies to https://github.com/pixijs/pixi.js/issues/3903).

* Moved measure function from TextStyle to Text and made static.

* Updated JSDocs.

* Updated JSDocs again.

* Updates based on suggestions by @bigtimebuddy in PR.

* Created PIXI.MeasuredText to capture all the information for measuring text.

* Fixes for ESLint

* Fixes for ESLint

* Added PIXI prefix to returning MeasuredText.

* Added import for MeasuredText in Text.js.

* Refactored MeasuredText to TextMetrics and moved `measure` function into it.

* Forgot to move Text.wordWrap to TextMetrics.wordWrap

* Further cleanup of TextMetrics.

* Fixes suggested by @bigtimebuddy

* Removed clone and equals from TextMetrics as they are unnecessary.

* Destructured references to TextMetrics instance in Text and privatized TextMetrics.wordWrap.

* Deprecates calculateFontProperties & getFontStyle

* Moved getFontStyle to TextMetrics

* Made toFontString method on TextStyle

* Cache calls made to context.measureText for individual characters

* Use a smaller (10x10) canvas for TextMetrics

Improvements to how and what is stored in the texture caches. (#3834) ...

* Improvements to how and what is stored in the texture caches.
Built upon the good work from https://github.com/pixijs/pixi.js/pull/3789
+ For Text, the base textures were in the BaseTextureCache, but textures weren't in the TextureCache. This has been fixed
+ Now able to tell the BaseTexture the origin of where the canvas being passed through has come from. ie. was it from the text class? was it from the graphic class? was it from caching as a bitmap? More information now to track where these canvases (canvii??) have been generated from
+ BaseTexture has addBaseTextureToCache and removeBaseTextureFromCache functions, to match regular Texture. Any adding or removing to the BaseTextureCache is now through these functions

! Breaking change. When you call Texture.fromTextureFromCache - it no longer automatically removes it's base texture from the base texture cache. Not sure how people feel about this

? I don't like lines 233 to 236 in Texture.js, and line 591 in BaseTexture.js - I don't see why they are there or why they are needed, but I chickened out on removing them!

* Renaming function to more generic names

* Adding deprecation layer

* Fixed trying to add texture to BaseTexture cache causing unit test fail

* Fixed reading from the wrong cache

* Able to remove textures and base textures from their caches via object instances
Added debug warning if trying to add a texture to a cache id that already exists
Added unit tests

* Default string for texture origin

* Different object creation style

* textureCacheId is now an array of potential entries

* textureCacheId changed to textureCacheIds

* Removed unneeded string creation

Should not apply padding when trimmed (#3858)

Able to set the alpha on Text drop shadows (#3651)

fix unexpected 0 text behaviour (#3650) ...

We got a weird glitch upgrading from pixi 3 to 4, setting the text in a PIXI.Text to 0 results in the label actually saying ' '. This seems like unexpected behaviour considering all the other numbers work :)

Fixed local bounds issue with text (#3633) ...

* Fixed local bounds issue with text

root cause of #3442

* lint..

Merge pull request #3622 from themoonrat/text-drop-shadow-blur-fix ...

Stops shadow blur appearing on the text as well as shadow

Merge pull request #3565 from staff0rd/Text_trim ...

Trimmed text

Ability to set stop points on Text with a gradient (#3576) ...

* Ability to set gradient stop points on Text

* little spacing consistency fix

* Better comparison of arrays

* Made fillGradientStopPoints clear they should be values between 0 and 1

* Potential fix for gradients

* making text with no set stops add the stops manually, so both settings take the same code path

fix type (#3627)

extract trim function to utils

Stops shadow blur appearing on the text as well as shadow ...

Does this by resetting this.context.shadowBlur both if it not required whilst drawing the shadow, and also after drawing the shadow
Fixes: https://github.com/pixijs/pixi.js/issues/3621

move trim to TextStyle

fix method name

added text trimming

Improved documentation ...

Class member documentation improved via removal of unnecessary @memberofs - more members now show up in the docs.
Class getter/setter documentation improved using technique above, and also by removing documentation for setters. Documentation was only showing the setter docs, whereas the getter is where the important information is. JSDoc maintainers themselves recommend just doccing the getter jsdoc3/jsdoc#973
Documented a few classes to let devs know that they are automatically created by PIXI and added to renderer.plugins, like interactionManager and prepare

Fix a bug about compute Text canvas size. (#3519) ...

* Fix a bug about compute Text canvas size.

There are 2 bugs :
* should NOT use `this.context.lineWidth`  before `this.context.lineWidth = style.strokeThickness`.
* the default value of `style.strokeThickness` is `0` , but  `this.context.lineWidth` couldn't be 0 ( in HTML5 , context.lineWidth = 0 will be ignore). So we should NOT use `this.context.lineWidth` for computing size.

* Update Text.js

Don't need  ` + style.strokeThickness` again.

* Update Text.js

* Update Text.js

refactor :   change the  codes of computing `canvas.width` & `canvas.height`  in the same code style.

* use  `style` instead of `this._style`

Merge pull request #3502 from finscn/patch-22 ...

The canvas could be passed into Text

Merge pull request #3513 from pixijs/multi-font-support ...

Adds support for multiple font families

Use `*._texture.*` instead of`*.texture.*` (#3517) ...

It could offer a bit little performance gains.

and in current version  https://github.com/pixijs/pixi.js/blob/master/src/core/text/Text.js#L637  , there is already used `_texture` .
So I think this patch is OK.

Less codes , Less assignment operations. ...

Remove the needless assignment operation.

Adds support for multiple font families

The canvas could be passed into Text ...

This feature could help users to  share canvas among two or more  Text  objects （ like Graphics._SPRITE_TEXTURE in Graphics).

In the game ,normally  we need rebuild stage/scene when stage/scene changed ,  If Text supports passing canvas , we could avoid create and destroy HTMLCanvasElement often when game running. 

e.g. create a canvas-pool  cache some canvas for Text.

Adds quotes around fontFamily (#3352)

Update documentation (#3337) ...

Parameter lines is a string array

fixed settings not being respected (#3315) ...

Discovered that using this kind of code:

```const { MY_SETTING } from settings;```

means that changing settings properties has no effect as the objects
are being set before the user changes them.

Moves constants that are actually settings (#3298) ...

* Made const that are setting writable

* Moved more items to the settings

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