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 :^)
* Remove unnecessary #include statements
* Move it into the TextEditor namespace
* Mark the single-argument constructor explicit
* Use move() to avoid some unnecessary copies
This allows the user to specify a specific line and column number to
start at when opening a file in TextEditor through the terminal, by
adding a colon after the file name.
For example, `TextEditor ReadMe.md:10:5` will open ReadMe.md and put
the cursor on line 10 at column 5.
To ensure that the user isn't trying to open a file that actually has
colons in its name, it checks if the file exists before parsing.
Replaces the feature added in b474f49164Closes#5589
