When the user has scrolled up and begins typing, the scrollbar will
automatically return them to the current cursor position so that they
can see what they're typing.
This was a workaround to be able to build on case-insensitive file
systems where it might get confused about <string.h> vs <String.h>.
Let's just not support building that way, so String.h can have an
objectively nicer name. :^)
This is not as perfect as it is elsewhere in the system, as we cannot
really change how terminal "thinks about" characters and bytes. What
we can do though, and what this commit does, is to *render* emojis, but
make it seem as if they take up all the space, and all the columns their
bytes would take if they were all regular characters.
We were checking the columns of the whole selection instead of the
the specfic line were modifying. Because of this, the selection
remained if the selection's column on another line was less than
the cursor.
This optimization was broken since who-knows-when. Now we once again do
our best to only repaint the lines that had the "dirty" flag set.
This dramatically reduces the amount of work done by an idle Terminal
since the cursor blinking won't redraw the whole window anymore. :^)
