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.Gpu/Engine/MME/IMacroEE.cs

@@ -7,7 +7,7 @@ namespace Ryujinx.Graphics.Gpu.Engine.MME
     /// <summary>
     /// FIFO word.
     /// </summary>
-    struct FifoWord
+    readonly struct FifoWord
     {
         /// <summary>
         /// GPU virtual address where the word is located in memory.

Ryujinx.Graphics.Gpu/Engine/MME/MacroHLETable.cs

@@ -13,7 +13,7 @@ namespace Ryujinx.Graphics.Gpu.Engine.MME
         /// <summary>
         /// Macroo High-level implementation table entry.
         /// </summary>
-        struct TableEntry
+        readonly struct TableEntry
         {
             /// <summary>
             /// Name of the Macro function.

Ryujinx.Graphics.Gpu/Engine/Threed/StateUpdateTracker.cs

@@ -11,7 +11,7 @@ namespace Ryujinx.Graphics.Gpu.Engine.Threed
     /// <summary>
     /// State update callback entry, with the callback function and associated field names.
     /// </summary>
-    struct StateUpdateCallbackEntry
+    readonly struct StateUpdateCallbackEntry
     {
         /// <summary>
         /// Callback function, to be called if the register was written as the state needs to be updated.