More consistent performance of breath marks. (issue 3821)

More consistent performance of breath marks. (issue 3821)

After tied notes, breaths take time only from the last note of the tie, so
e.g. { c4 ~ c8 \breathe } performs as { c4 ~ c16 r }, not { c4 r8 }.
This is consistent with articulations, and with how humans interpret
breaths after ties. This makes it possible to align simultaneous
breaths in multiple parts with different note lengths.

Ignore grace time when calculating the length of the note before a breath —
subsequent grace notes take time from the breath, not the previous note.