ui: use stencil buffer to draw polygons (#28902)

* Update ui.cc

* add a bunch of debugging stuff i don't want to lose

* Revert "add a bunch of debugging stuff i don't want to lose"

This reverts commit 2de6ab5b68.

* enable stencil buffer

* lower ui CPU usage

* Revert "lower ui CPU usage"

This reverts commit 650241c0d8.

selfdrive/ui/qt/util.cc

@@ -96,6 +96,7 @@ void setQtSurfaceFormat() {
   fmt.setRenderableType(QSurfaceFormat::OpenGLES);
 #endif
   fmt.setSamples(16);
+  fmt.setStencilBufferSize(1);
   QSurfaceFormat::setDefaultFormat(fmt);
 }