Support pixi/phaser like filters

[Jerry457]

The current materials can do some of it but it requires you to fully rewrite the shader that usually don't work with other built-in actions like tint and flash (this is essentially a PostProcessor for a single Actor), it is also hard to do thing like glow and outlines which require a certain amount of padding around the image/graphics

It would be nice to also add some commonly used ones like glow, color matrix, ...

[eonarheim]

@Jerry457 Totally agree, this is 100% on my list. I have a now defunct branch where I attempted this type of thing. The idea is to have composable shaders like pixi filters.

I'll be retackling this issue based on what I learned doing this, roughly it means adding render targets to everything so we can apply shaders to everything (and possibly cache). https://github.com/excaliburjs/Excalibur/pull/3364