Chore: Cleanup useContextAlpha deprecation

[bigtimebuddy]

Closes #8861

Changed

• Removes useContextAlpha from the Application, CanvasRenderer and Renderer options documentation
• Add deprecation flag to useContextAlpha in IRenderOptions
• Always set a default for premultipliedAlpha as this is now a required field
• Add deprecation warnings and fallback behavior for useContextAlpha with constructor arguments

[SuperSodaSea]

By the way, the deprecation message seems to be incorrect here:

pixijs/packages/core/src/Renderer.ts

Lines 549 to 561 in 6d10e13

	/**
	* This sets weather the screen is totally cleared between each frame withthe background color and alpha
	* @deprecated since 7.0.0
	*/
	get clearBeforeRender(): boolean
	{
	// #if _DEBUG
	// eslint-disable-next-line max-len
	deprecation('7.0.0', 'renderer.useContextAlpha has been deprecated, please use renderer.background.clearBeforeRender instead.');
	// #endif
	return this.background.clearBeforeRender;
	}