SDL: Change keyboard repeat to apply on unmapped events

The keyboard repeat event generator is used when building against SDL1.
Previously the repeat events would generate based on the event stream
produced by the keymapper which is not guaranteed to have matching up
and down events in the case the keymaps are changed while a key is
pressed.

Fixes #11417.

backends/platform/sdl/sdl.h

@@ -117,6 +117,7 @@ protected:
 	 * The event source we use for obtaining SDL events.
 	 */
 	SdlEventSource *_eventSource;
+	Common::EventSource *_eventSourceWrapper;
 
 	/**
 	 * The SDL output window.