Better support for bend/falls

Task description

Our current support for bend/falls is admittedly quite poor. They can be edited in the score, but the line thickness can't be edited (in fact, the property panel displays nothing for these items).

So I would say:

• TASK 1: Make the thickness of bend/falls line an editable property (and consider if there are other properties that would be worth exposing there).

Second: the lines we provide are draw in-software, but we should also consider that there are dedicated SMUFL glyphs for these shapes, which look much better (and are designed to go with the music font, so jazz fonts have their own thicker ones etc). Of course the downside of those is that they can't be edited. Anyway, these glyphs can be now found and inserted via the master palette, but their default position isn't optimized.

So I would say:

• TASK 2: Move the Smufl glyphs for bends/falls into the same palette, so they are more discoverable.
• TASK 3: Make sure that their default position makes sense.

See #16246 for some examples.