AOT Support?

[HurricanKai]

This PR includes the barebones support for AOT CoreRT and modifies the sample in Labs to function.

Changes include:

• Window & InputWindowExtension changes to allow disabling of the default first party support. (This also means platforms are now lazy loaded)
• 1 new Type with one function in each of SDL/GLFW input & windowing that adds the platform. (These are the only visible types in that namespace, not sure if desirable)
• Adds .net 5 as build target to all projects, this means .net 5 will propagate through projects and dependencies, making it possible to enable features on .net 5 and higher only. This has been long overdue imo.

[Perksey]

I wouldn't set projects to multi target unless it actually has .NET 5-specific enhancements. NuGet is smart enough to get a .NET 5 version of a package even if the referencing package only targets .NET Standard 2.0, but the dependency cross-targets.

[HurricanKai]

Didn't know NuGet was that smart. I'd preferably keep all the multi-targeting to allow the possibility for the future. I plan on optimizing a lot of stuff with the awesome new features.
If you prefer, I'll remove the multi-targeting here, and re-add it once needed?

[Perksey]

If you prefer, I'll remove the multi-targeting here, and re-add it once needed?

This sounds like the preferred way to go.

[Perksey]

All of the unanswered comments from above, and...

[HurricanKai]

Rebased onto origin/2.0 to get the RC1 changes. Git kinda died so I had to force push 😅