Support URP

[GlaireDaggers]

May be worth taking a look at directly supporting URP. I have some amount of disdain for it, but it's what Unity is pushing and so probably worth ensuring it's supported.

[GlaireDaggers]

According to @YooPita this might turn out more complicated than expected. Will have to investigate further. Should treat this as low priority compared to the upgrade.

[GlaireDaggers]

Since the upgrade is done and I even have an experimental package-ified branch ready to go, I decided to take a chance to investigate this.

It seems like this might actually be doable with a custom ScriptableRenderPass, I already got a custom post processing effect working this way. The main challenge is that the render pass works via command buffers, so likely a good deal of code would have to be extracted out of CRT Effect and modified to work with a command buffer style setup.

There IS another complicating factor here, though, which is the low res / pixel effect. It's still possible, but it gets kinda hacky. Setup basically involves having a render camera rendering into a target texture, using one renderer, and then the main camera using a custom render feature to blit that target texture to the screen using another renderer. Not the worst, but definitely more setup than the builtin renderer.

EDIT: TBH I feel like further investigation probably ought to be held off until I decide whether I want to go through with the package manager conversion, so I can decide how I'm going to structure this in a way that doesn't break the core package if URP isn't present.