Certains keys (such as ~ and |) are in the keyboard map behind the
second shift level. This means in order for them to be input, the
shift key needs to be held down by the user.
The GNOME Shell on-screen keyboard presents these keys separately on
a page of keys that has no shift key. Instead, it relies on mutter
to set a shift latch before the key event is emitted. A shift latch
is a virtual press of the shift key that automatically gets released
after the next key press (in our case the ~ or | key).
The problem is using a shift latch doesn't work very well in the face
of key repeat. The latch is automatically released after the first
press, and subsequent repeats of that press no longer have shift
latched to them.
This commit fixes the problem by using a shift lock instead of a shift
latch. A shift lock is never implicitly released, so it remains
in place for the duration of key repeat.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2045>
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