[MU4 Issue] Improve horizontal position of chord tie endpoints

[oktophonie]

• add an option to start ties after augmentation dots, where present;
• on left, take into account bounding boxes of all elements of starting chord: flags, ledger lines, stems, offset noteheads, dots (if the aforementioned option has been chosen), etc.;
• on the right, take into account bounding boxes of all elements of the ending chord, similarly (dots and flags will not be relevant).

It appears that horizontal placement is determined first, and that this is dependent on the available space, and therefore can change when the music is respaced (at least for now); the horizontal offsets will need to be recalculated then too.

Some approximate before-and-afters:

This is a first step towards addressing https://musescore.org/en/node/45576 and many of the issues linked there. (Horizontal position, curvature, behaviour for single notes etc. all to follow.)