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/Cache/CacheEntry.cs

@@ -4,7 +4,7 @@ using System.Diagnostics.CodeAnalysis;
 
 namespace ARMeilleure.Translation.Cache
 {
-    struct CacheEntry : IComparable<CacheEntry>
+    readonly struct CacheEntry : IComparable<CacheEntry>
     {
         public int Offset { get; }
         public int Size   { get; }

ARMeilleure/Translation/Cache/CacheMemoryAllocator.cs

@@ -6,7 +6,7 @@ namespace ARMeilleure.Translation.Cache
 {
     class CacheMemoryAllocator
     {
-        private struct MemoryBlock : IComparable<MemoryBlock>
+        private readonly struct MemoryBlock : IComparable<MemoryBlock>
         {
             public int Offset { get; }
             public int Size { get; }

ARMeilleure/Translation/CompilerContext.cs

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

ARMeilleure/Translation/RegisterUsage.cs

@@ -14,7 +14,7 @@ namespace ARMeilleure.Translation
         private const int RegsCount = 32;
         private const int RegsMask  = RegsCount - 1;
 
-        private struct RegisterMask : IEquatable<RegisterMask>
+        private readonly struct RegisterMask : IEquatable<RegisterMask>
         {
             public long IntMask => Mask.GetElement(0);
             public long VecMask => Mask.GetElement(1);

ARMeilleure/Translation/Translator.cs

@@ -293,7 +293,7 @@ namespace ARMeilleure.Translation
             }
         }
 
-        private struct Range
+        private readonly struct Range
         {
             public ulong Start { get; }
             public ulong End { get; }