Merge remote-tracking branch 'upstream/dev' into more_container_tests

use worldAlpha

Update docs: issue #3085 ...

#3090: Putting this out here. After encountering #3085 this is what I found. Please feel free to revise as needed, as I admit my knowledge on the matter is limited. I hope it helps someone else.

remove superfluous check

Bypass the getter / setter for anchor inside Sprite

Restore lost context before using it; fixes #2958 ...

Looks like since we call loseContext() on `WebGLRenderer#destroy()` that
if you create another WebGLRenderer with the same canvas the browser will
recycle that lost context and return it.

This means when we try to use the context it is actually in a lost state.
This change tries to restore a lost context before we use it. It also adds
a debug assert at one location that will be invalid if the context is
invalid.

Merge pull request #3060 from englercj/fix-image-url-detect ...

Replace url extension regex

remove some changes from texture

1. moved clamping into TextureTransform ...

2. texture now has an optional component

some restructuring

Clamping is magic

clamping is hilarious ...

THIS IS THE PAIN

Giant tilingSprite refactoring. ...

1. Rotated and trimmed textures are allowed
2. "full" textures use simple shader if they have WRAP_MODE.REPEAT
3. WRAP_MODE.REPEAT is forced if that texture uploads in TilingSprite first time
4. TilingSprite now has tileTransform which applies to the "zero tile" like if its been a child

replace url extension regex; fixes #3059

Improvement of PR #3053

Merge pull request #3053 from staff0rd/addChildAt_fix ...

Allow Container.addChildAt when zero children

fixes #3055

allow Container.addChildAt when zero children

Fix #2971; merges #3046

Merge pull request #3043 from themoonrat/video-base-texture ...

VideoBaseTexture fixes and changes

strange imports problem

_parentID was not in the class. Hidden class problem

fix for #3027

VideoBaseTexture fixes and changes ...

* https://github.com/pixijs/pixi.js/commit/8d39e810c595b0afc48e542b2d4cad9c204cc7d2 didn't fully solve the video loading issues; the examples page for videos still doesn't work. I've tracked that down to the static 'fromUrl' function, which called video.play(). This was a tad early, resulting in width and height being 0. Removing the .play here doesn't matter, as it is still automatically called within _onCanPlay()
* autoUpdate changed to a getter/setter. It's previous doc stated that it could be used to control when autoUpdating happened, but this wasn't true, it was actually just an internal variable to check whether it was currently auto updating or not. I've create a couple of private tracking variable for the state, whilst the public getter / setting now truely controls autoUpdating and can be changed on the fly.
* moved this class to use the ticker. My expectation as a dev is that if I stop the shared ticker, PIXI would stop, but VideoBaseTexture was an exception as it used rAF directly.

Fixed variable naming issue reported in #2903 (#3035)

Smaller default texture size for text (#3036)

updated some doc comments (#3038)

Fix some loading issues; fixes #2687

Merge pull request #3032 from rkrasky/patch-5 ...

onAnchorUpdate function is private with underscore

onAnchorUpdate function is private with underscore ...

onAnchorUpdate function is private with underscore