Add an option to present/skip presenting duplicate frames

Currently, we do not display every second frame in 25fps/30fps games
which run to vsync. This improves performance as there's less rendering
for the GPU to perform, but when combined with vsync, could cause frame
pacing issues.

This commit adds an option to force every frame generated by the console
to be displayed to the host, which may improve pacing for these games.

Source/Android/app/src/main/res/values/strings.xml

@@ -232,6 +232,8 @@
     <string name="xfb_copy_method_description">Stores XFB Copies exclusively on the GPU, bypassing system memory. Causes graphical defects in a small number of games that need to readback from memory. If unsure, leave this checked.</string>
     <string name="immediate_xfb">Immediately Present XFB</string>
     <string name="immediate_xfb_description">Displays the XFB copies as soon as they are created, without waiting for scanout. Causes graphical defects in some games but reduces latency. If unsure, leave this unchecked.</string>
+    <string name="skip_duplicate_xfbs">Immediately Present XFB</string>
+    <string name="skip_duplicate_xfbs_description">Skips presentation of duplicate frames. This may improve performance on low-end devices, while making frame pacing less consistent. If unsure, leave this checked.</string>
     <string name="disable_destination_alpha">Disable Destination Alpha</string>
     <string name="disable_destination_alpha_description">Disables emulation of a hardware feature called destination alpha, which is used in many games for various effects.</string>
     <string name="fast_depth_calculation">Fast Depth Calculation</string>