Reduce usage of Marshal.PtrToStructure and Marshal.StructureToPtr (#3805)

* common: Make BinaryReaderExtensions Read & Write take unamanged types

This allows us to not rely on Marshal.PtrToStructure and Marshal.StructureToPtr for those.

* common: Make MemoryHelper Read & Write takes unamanged types

* Update Marshal.SizeOf => Unsafe.SizeOf when appropriate and start moving software applet to unmanaged types

Ryujinx.HLE/HOS/Applets/SoftwareKeyboard/SoftwareKeyboardCustomizeDic.cs

@@ -5,10 +5,9 @@ namespace Ryujinx.HLE.HOS.Applets.SoftwareKeyboard
     /// <summary>
     /// A structure used by SetCustomizeDic request to software keyboard.
     /// </summary>
-    [StructLayout(LayoutKind.Sequential, Pack = 4)]
+    [StructLayout(LayoutKind.Sequential, Size = 0x70)]
     struct SoftwareKeyboardCustomizeDic
     {
-        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 112)]
-        public byte[] Unknown;
+        // Unknown
     }
 }