Port yuzu-emu/yuzu#9300: "CMake: Use precompiled headers to improve compile times" (#6213)

Co-authored-by: Ameer J <52414509+ameerj@users.noreply.github.com>

src/citra_qt/precompiled_headers.h

@@ -0,0 +1,7 @@
+// Copyright 2022 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include "common/common_precompiled_headers.h"