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/IntermediateRepresentation/PhiOperation.cs

@@ -3,7 +3,7 @@ using static ARMeilleure.IntermediateRepresentation.Operand.Factory;
 
 namespace ARMeilleure.IntermediateRepresentation
 {
-    struct PhiOperation
+    readonly struct PhiOperation
     {
         private readonly Operation _operation;