Some terminals send the focus-in sequences ("^[I") whenever focus reporting is
enabled. We enable focus reporting whenever we are finished running a command.
If we run two commands without reading in between, the focus sequences
will show up on the terminal.
Fix this by enabling focus-reporting as late as possible.
This fixes the problem with `^[I` showing up when running "cat" in
gnome-terminal https://github.com/fish-shell/fish-shell/issues/10411.
This begs the question if we should do the same for CSI u and bracketed paste.
It's difficult to answer that; let's hope we find motivating test cases.
If we enable CSI u too late, we might misinterpret key presses, so for now
we still enable those as early as possible.
Also, since we now read immediately after enabling focus events, we can get
rid of the hack where we defer enabling them until after the first prompt.
When I start a fresh terminal, the ^[I no longer shows up.
`read` allows specifying the initial command line text. This was
text got accidentally ignored starting in a32248277f. Fix this
regression and add a test.
Fixes#8633
Note: This includes a super cheesy thing to print variable contents.
The expect version has one that's a bit more elaborate (featuring a
marker setup), but tbh that doesn't seem to be worth it.
If we do need it, we can add it, but it seems more likely we'd just do
`set -S`, or do it in a check instead.
