Add a configuration key for the TERM environment variable. Default this
to "ghostty". Most TEs are using their name as the default TERM value.
Most modern termulators aren't even providing "xterm-" as an alias
anymore, after some drama between kitty / ncurses.
Notably, this also has issues for tcell-based applications (I've
submitted a PR to tcell to fix) because it fails if the TERM value
doesn't match the _primary_ name of the terminal in the terminfo file.
Providing a config option allows users to modify-with-persistence if
they have issues, but Ghostty should be known as Ghostty by default!
These OSC commands report the default foreground and background colors.
Most terminals return the RGB components scaled up to 16-bit components, because some
legacy software are unable to read 8-bit components. The PR follows this conventions.
iTerm2 allow 8-bit reporting through a config option, and a similar option is
added here. In addition to picking between scaled and unscaled reporting, the user
can also turn off OSC 10/11 replies altogether.
Scaling is essentially c / 1 * 65535, where c is the 8-bit component, and reporting
is left-padded with zeros if necessary. This format appears to stem from the XParseColor
format.
