fix(core): emit keystroke was writing to wrong queue

Fixes #7649.

emit_keystroke code path in kmx processor was writing directly to the
core queue instead of to the internal kmx processor queue. This caused
it to be out-of-order in the actions sent to the engine/debugger.

Engines didn't really care but it broke the debugger, for example if
only a deadkey was in the buffer and backspace was pressed, Developer
would assert as it would get unexpected context for the deletions.