If a mouse position was above the maximum supported by the normal mouse

If a mouse position was above the maximum supported by the normal mouse
protocol (223), tmux was allowing it to wrap around. However, since tmux
was not correctly handling this on input, other programs also do not
handle it correctly, and the alternative SGR mouse mode is now
widespread, this seems unnecessary, so remove this feature. Also define
some constants to make it clearer what the numbers mean. Mostly from
Leonid S Usov in GitHub issue 3165.