runtime(menu): define shortcut for File->Open Tab (#12895) Commit: https://github.com/vim/vim/commit/e059fae100448fee4b581dd5d90ee853ea18de7e Author: Christian Brabandt <cb@256bit.org> Date: Wed Aug 23 17:07:55 2023 +0100 runtime(menu): define shortcut for File->Open Tab (https://github.com/vim/vim/issues/12895) Seems missing as noted by Antonio Giovanni Colombo. So add it and use the 'T' as shortcut, which does not seem to be used in the File dialog. Verified on Windows. Signed-off-by: Christian Brabandt <cb@256bit.org> Co-authored-by: Antonio Giovanni Colombo <azc100@gmail.com>