Fix password entry jumping to different networks with wifi scanning, by pausing the scan when appropriate

Fixes the problem where the password entry jumps to a different network if the order of network signal strengths changes while typing the password.

I saw this bug on an /r/linux post: https://old.reddit.com/r/linux/comments/kld6t7/2021_will_be_year_of_linux_on_the_desktop/. To my knowledge this has not been reported on bugs.kde.org.

The fix is somewhat crude, it just pauses the scan timer while a password entry box has active focus.

I tried other approaches, such as making the highlight follow the network as it is shuffled around (this turned out to be infeasible since multiple networks can be expanded at the same time etc).

@ndavis suggested scanning in the background while it is paused, but that turns out to be infeasible too since the QML view is directly linked to the network list in the backend, thus updating the network list without changing the UI can't be done within the current architecture of the applet.

I have tested if it fixes the bug, and it seems to work as intended, but the networks near me aren't as volatile as the original reporter's, so I haven't been able to test it in the intended conditions. So I have messaged some people who claimed to also have the bug, asking them to help test the fix. Hopefully it works on their machines as well.

EDIT: sorry if I messed up the git commits, I'll make a new branch/MR if neccessary.