Replaces `set_tooltip_deprecated(string);` with
`set_tooltip(MUST(String::from_deprecated_string(string)));`
purely to get rid of the deprecated function in the following commit.
Instead of poking into the the applet window backing store whenever
the keymap changes, we now drive the GUI updates properly via
update() and paint_event().
This fixes an issue where changing the system font would cause a
"ghosting" effect in the keymap applet.
In 7c5e30daaa, the focus was "only" on
Userland/Libraries/, whereas this commit cleans up the remaining
headers in the repo, and any new badly-formatted include.
We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)
