This will make it easier to support both string types at the same time
while we convert code, and tracking down remaining uses.
One big exception is Value::to_string() in LibJS, where the name is
dictated by the ToString AO.
Each of these strings would previously rely on StringView's char const*
constructor overload, which would call __builtin_strlen on the string.
Since we now have operator ""sv, we can replace these with much simpler
versions. This opens the door to being able to remove
StringView(char const*).
No functional changes.
Previously, when you selected to have a custom format, whatever was in
the custom-format box would get replaced with the format for
12-hour-without-seconds. Now, it keeps whatever was in the box before -
which is less disorientating, and lets you tweak the existing format.
This means that if you save and close ClockSettings with "24-hour"
and "Show seconds" both checked, then they will both be checked when
you re-open ClockSettings, instead of it showing as a "Custom" format.
This renames the current implementation of current_time_zone to
system_time_zone to more clearly indicate what it is. Then reimplements
current_time_zone to return whatever was set up by tzset, falling back
to UTC if something went awry, for convenience.
