A few doc updates (#3527)

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

correct blob parser import

Update to Resource loader v2; fixes #2876

Fixed doc style for typed array

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

Use `*._texture.*`to instead of`*.texture.*` (#3508) ...

it could offer a bit little performance gains.

limit alpha number to 255. at rendering. (#3511) ...

* limit alpha number to 255. at rendering.

Avoid alpha flickering when it passes 1.0

* added space after comma

Use `this._texture.X`to instead of`this.texture.X` (#3480) ...

In get/set width/height method , we don't need use  `this.texture` .

We could use `this._texture.X`to instead of`this.texture.X` , and it could offer a bit little performance gains.

Remove a needless space in annotation (#3497)

Protect the initial state of `this._activeRenderTarget` in _indexContext (#3443) ...

* Update WebGLRenderer.js

```
    this._activeRenderTarget = null;
    this._activeTextureLocation = 999;
    this._activeTexture = null;
````
must before `this._indexContext()` , otherwise  the _activeRenderTarget & _activeTexture init in  _indexContext will back to `null`.

* Add a blank line for cosmetic.

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.

docs fix for TextureTransform (#3498)

Update annotation: `SpriteBatch to SpriteRenderer` (#3496) ...

* Update annotation: `SpriteBatch to SpriteRenderer`

PIXP 4.x  no SpriteBatch

* more

Code Formatting (#3484) ...

Format some codes.

Haven't changed any logic.

Update `clear` for a more thorough cleaning (#3445) ...

* Update `clear` for a more thorough cleaning

Clear something that should be cleared.
`
        this.currentPath = null;
        this._spriteRect = null;
`
if no this patch , some test cases will be failed.


##Test Case
There is some common codes of test cases :
```js
var renderer = new PIXI.WebGLRenderer(900, 600, {
    clearBeforeRender: false,
    backgroundColor: 0xFFFFFF
});
document.body.appendChild(renderer.view);

// the root container.
var stage = new PIXI.Container();
```

### TEST 1
If no  ```currentPath = null ``` ,  the second arc can't be rendered, and there is no error on browser's console.

```js

    var graphics = new PIXI.Graphics();
    stage.addChild(graphics);

    // clear manually
    renderer.clear();

    graphics.clear();
    graphics.beginFill(0xFF0000);
    graphics.arc(150, 160, 100, 0, Math.PI * 2, false);
    graphics.endFill();

   // draw  the first shape
    renderer.render(stage);

    graphics.clear();
    graphics.beginFill(0x0000FF);
    graphics.arc(150+50, 160+50, 100, 0, Math.PI * 2, false);
    graphics.endFill();

   // draw  the second shape
    renderer.render(stage);
```

### TEST 2
If no  ```_spriteRect = null ``` ,  the first rect can't be rendered, and there is no error on browser's console.

```
    var graphics = new PIXI.Graphics();
    stage.addChild(graphics);

    // clear manually
    renderer.clear();

    graphics.clear();
    graphics.beginFill(0xFF0000);
    graphics.drawRect(150, 160, 100, 60);
    graphics.endFill();

    // draw the first shape
    graphics.updateTransform();
    graphics.renderWebGL(renderer);

    graphics.clear();
    graphics.beginFill(0x0000FF);
    graphics.drawRect(150+50, 160+50, 100, 60);
    graphics.endFill();

    // draw the second shape
    graphics.updateTransform();
    graphics.renderWebGL(renderer);

    // flush manually
    renderer.flush();
```

### Summary

If don't call  `graphics.clear();` before draw the second shape , there will be another error.

If add 
```
        this.currentPath = null;
        this._spriteRect = null;
```
in `clear()` everything will be OK, and I test many other examples, this patch doesn't break anything else, it's safe.


I know when we want to draw multi shapes , we could use multi graphics objects.
But we shouldn't prevent users to use one shared graphics to draw multi shapes.

* Remove trailing spaces.

Test case & fix for Graphics._calculateBounds calling updateLocalBounds every time (#3444) ...

* Test case for #3414

* Fixes #3414

* fixed expectation

Do not unload generated textures when manually running the texture garbage collector. This already happens when it is run automatically, as it will cause the texture to not be able to be renderered again (#3342)

Allow '0x' notation of colours via strings to work in Text class (#3341) ...

* Allow strings representing values such as '0xFFFFFF' to be parsed and used by the Text class

* Removed es6 string includes function

Add parameter kernelSize for blur filters. (#3410) ...

* Add parameter kernelSize for blur filters.

* update annotation: remove option 3

* fixed typo.

* update annotation

target clarification (#3470)

Fixes logic for spritesheet resolution (#3464) ...

* Fixes logic for spritesheet resolution

* Typo

* Fixes default logic

* Added an inline comment about the resolution

expose moveWhenInside docs (#3471)

Change the lines order in updateTransform. (#3435) ...

Change the lines order in updateTransform for unified style

see 
https://github.com/pixijs/pixi.js/pull/3404
https://github.com/pixijs/pixi.js/pull/3391

fix for regular transform (#3424) ...

* fix for regular transform

_ removed for non observable points

* fixed for local update transform

Customize rendering process with "pluginName" field. (#3413) ...

* Customize rendering process with "pluginName" field.

Change the code lines order in updateTransform in TransformStatic.js (#3404) ...

* Update TransformStatic.js

```
            const pt = parentTransform.worldTransform;
            const wt = this.worldTransform;
```
the code above in updateTransform  is not needed always.

And another reason is like  https://github.com/pixijs/pixi.js/pull/3391

* Update TransformStatic.js

remove the trailing-spaces.