Make structs readonly when applicable (#4002)

* Make all structs readonly when applicable. It should reduce amount of needless defensive copies

* Make structs with trivial boilerplate equality code record structs

* Remove unnecessary readonly modifiers from TextureCreateInfo

* Make BitMap structs readonly too

ARMeilleure/Translation/CompilerContext.cs

@@ -2,7 +2,7 @@ using ARMeilleure.IntermediateRepresentation;
 
 namespace ARMeilleure.Translation
 {
-    struct CompilerContext
+    readonly struct CompilerContext
     {
         public ControlFlowGraph Cfg { get; }