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`

tests/cefclient/browser/osr_render_handler_win_gl.cc

@@ -131,7 +131,7 @@ void OsrRenderHandlerWinGL::OnAcceleratedPaint(
     CefRefPtr<CefBrowser> browser,
     CefRenderHandler::PaintElementType type,
     const CefRenderHandler::RectList& dirtyRects,
-    void* share_handle) {
+    const CefAcceleratedPaintInfo& info) {
   // Not used with this implementation.
   NOTREACHED();
 }