If the shift key was pressed, we should switch back to the default level
after the next commit. It seems that this only worked due to a superfluous
signal emission so far (see https://gitlab.gnome.org/GNOME/mutter/-/issues/3448).
When the keyboard is in this "shift" level (note: only "shift", not
"opt+shift" level) without being latched, there are certain events that
should put it back into the default level:
- A normal character key on the OSK being pressed
- A keyval on the extended OSK (eg. TAB key or an arrow key) being pressed
- The backspace key being pressed
- The OSK being hidden
- The user moving focus in the entry
The `_updateLevelFromHints()` function already takes care of updating the
active level after certain kinds of events, we can achieve the desired
behavior by adding a fallback case to that function where it moves the level
back from "shift" to "default".
Since we only want this switch back to the "default" layer as a response to
actual user input, add a `userInputHappened` boolean to
`_updateLevelFromHints()` and don't set that when the application simply
changes its content hints.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3286>
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