[X11] Reconcile logical keyboard state with physical state on FocusIn

since the window system doesn't do it for us like other platforms.

This prevents sticky keys and missed keys when going in and out
of focus, for example Alt would appear to stick if switching away
from an SDL app with Alt-Tab and had to be pressed again.

CR: Sam

visualtest/unittest/testquit.parameters

@@ -0,0 +1,3 @@
+--exit-code, integer, [-1 1], false, [] # The exit code returned by the executable
+--crash, boolean, [], false, [] # Crashes the SUT executable
+--hang, boolean, [], false, [] # Runs the SUT in the infinite loop and ignores all events