Make \tweak useful on chord repetitions

This makes \tweak have an effect on "q" just like if the original chord were written out and tweaked. Since there are no elements in the chord repetition at the time \tweak operates, it now stores the tweak list in the chord itself. Then the infrastructure that replaces "q" with the last chord also takes care of propagating tweaks. This follows the implementation sketch suggested by David, see https://lists.gnu.org/archive/html/lilypond-user/2022-11/msg00014.html