MSL shader support

[squidbus]

Backport of MSL support from the Marathon fork of XenosRecomp, which in turn is based on @IsaacMarovitz's work (#15) with some additional tweaks and fixes.

• Generates shader code that is both valid HLSL and MSL.
  • This required some extra work in the compiler to perform things like input/output size tracking for correct vector type casts.
• Compiles to Metal AIR using Xcode tools.
  • Unfortunately cannot include source info for debugging using code-based shader compilation, which would make it impossible to see shaders in the Metal debugger.
• Misc backports:
  • Fix for SetpInv logic.
  • tfetchTexcoord -> swapFloats for generic use by projects needing to swap other attributes.
  • Generates shader names in cache table for debugging purposes.

This has been tested with both MarathonRecomp and UnleashedRecomp.