osr: Implement shared texture support (fixes #1006, fixes #2575)

Adds support for the OnAcceleratedPaint callback. Verified to work
on macOS and Windows. Linux support is present but not implemented
for cefclient, so it is not verified to work.

To test:
Run `cefclient --off-screen-rendering-enabled --shared-texture-enabled`

patch/patch.cfg

@@ -772,5 +772,14 @@ patches = [
     # views: mac: Add customization point to acceptsFirstMouse.
     # https://github.com/chromiumembedded/cef/issues/3680
     'name': 'mac_render_widget_3680'
+  },
+  {
+    # win: Remove keyed mutex with OSR for better performace and to avoid
+    # potential vendor driver bugs.
+    # https://bitbucket.org/chromiumembedded/cef/pull-requests/734
+    # https://github.com/chromiumembedded/cef/issues/2575
+    # It is a bit hacky, not suitable for merging into upstream.
+    # https://chromium-review.googlesource.com/c/chromium/src/+/5302103
+    'name': 'osr_win_remove_keyed_mutex_2575'
   }
 ]