EXPERIMENTAL: Metal backend (#441)

This is not a continuation of the Metal backend; this is simply bringing
the branch up to date and merging it as-is behind an experiment.

---------

Co-authored-by: Isaac Marovitz <isaacryu@icloud.com>
Co-authored-by: Samuliak <samuliak77@gmail.com>
Co-authored-by: SamoZ256 <96914946+SamoZ256@users.noreply.github.com>
Co-authored-by: Isaac Marovitz <42140194+IsaacMarovitz@users.noreply.github.com>
Co-authored-by: riperiperi <rhy3756547@hotmail.com>
Co-authored-by: Gabriel A <gab.dark.100@gmail.com>

src/Ryujinx.Graphics.Shader/StructuredIr/HelperFunctionsMask.cs

@@ -7,7 +7,14 @@ namespace Ryujinx.Graphics.Shader.StructuredIr
     {
         MultiplyHighS32 = 1 << 2,
         MultiplyHighU32 = 1 << 3,
+
+        FindLSB = 1 << 5,
+        FindMSBS32 = 1 << 6,
+        FindMSBU32 = 1 << 7,
+
         SwizzleAdd = 1 << 10,
         FSI = 1 << 11,
+
+        Precise = 1 << 13
     }
 }