fix: add more options for screen sharing frame rate

Currently, the maximum frame rate of screen sharing is only 25fps.
Add more options to increase the maximum frame rate.

This PR fixes issue #1851.

Workaround for https://bugreports.qt.io/browse/QTBUG-54767 or
https://bugreports.qt.io/browse/QTBUG-130996.

This is probably the worst code I have written in a while, but basically
we add a value interceptor to filter out any invisible menu entry. This
is pretty dangerous because one false step crashes the whole menu. Menu
entries are actually Cpp owned and need to be manually deleted unless
they are removed via removeItem. Care needs to be taken to not mess up
the contentData list.

I expect this to break soon.

Otherwise we might get stuck on requests exceeding the server side size
limits forever.

grammar fix for untrusted source message

refactor: use fmt lib to avoid back-and-forth conversion

Add profile name to tooltip & fix message count

This will look bad on some platforms and older versions for now, but
should fix a lot of crashes and we can report the rest as bugs.

This is causing probably more issues nowadays than it fixes. Qt should
be adding those menus for us now, so let's remove it and see, what
breaks!

Always allow sending messages by enter even with IMEs

Do not fetch Qt from Debian experimental when building for Qt6

Qt version in Debian Trixie is 6.6 as of September 2024. Therefore there
is no need to use experimental repositories.