GUAC-862: Perform sanity checks on legacy keyIdentifier. Only release Ctrl+Alt if it appears to be a simulated AltGr based on detected keysym.
GUAC-862: Prefer keyCode to DOM3 key for keyup, as it's more accurate when dead keys are used.
GUAC-862: Simplify keydown logic. Restore workaround for Chrome meta bug.
GUAC-862: Restore handling of keyCode 229 (composition).