citra-qt: Enable high-DPI widgets on Mac app

The OS will render the widgets using the system screen DPI (instead of
being locked at @1x resolution).

This has no impact on the existing high-DPI rendering code in Citra,
which means that the resolution of the emulated content is increased
to the real number of pixels, as on other platforms.

src/citra_qt/Info.plist

@@ -32,5 +32,9 @@
 	<true/>
 	<key>NSHumanReadableCopyright</key>
 	<string></string>
+	<key>NSPrincipalClass</key>
+	<string>NSApplication</string>
+	<key>NSHighResolutionCapable</key>
+	<string>True</string>
 </dict>
 </plist>