Implement and use MOVZX(64, 32,...)

Probably better to keep that same-register-MOV assert useful. Also,
explicit type extension documents whats happening.

Internally, this boils down to the original MOV, but without the assert.

Source/Core/Common/Src/x64Emitter.cpp

@@ -768,6 +768,10 @@ void XEmitter::MOVZX(int dbits, int sbits, X64Reg dest, OpArg src)
 		Write8(0x0F);
 		Write8(0xB7);
 	}
+	else if (sbits == 32 && dbits == 64)
+	{
+		Write8(0x8B);
+	}
 	else
 	{
 		Crash();