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 :^)
Because of how we output lines in the loop above, if we leave that loop
when the last line was not the same in both files, then either
`file1_line` or `file2_line` has not been output yet.
`process_remaining()` does not print that line either, since it
immediately reads a new line. So, output the previously-missing line
before we call that. :^)
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.
