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

Ryujinx.Graphics.Shader/Translation/FunctionMatch.cs

@@ -87,7 +87,7 @@ namespace Ryujinx.Graphics.Shader.Translation
             }
         }
 
-        private struct TreeNodeUse
+        private readonly struct TreeNodeUse
         {
             public TreeNode Node { get; }
             public int Index { get; }
@@ -345,7 +345,7 @@ namespace Ryujinx.Graphics.Shader.Translation
             bool Matches(in InstOp opInfo);
         }
 
-        private struct PatternTreeNodeUse
+        private readonly struct PatternTreeNodeUse
         {
             public IPatternTreeNode Node { get; }
             public int Index { get; }