Fix #21110 - position the text of glissando according to its physical sizes and no longer by a hard-coded vert. offset

It should also fix #20970: collision of glissando with ledger lines.
Smarter algorithm for avoiding collision with start note ledger line.

Added detection of start note dot(s).
Improving dot width detection
Merge pull request #367 from mgavioli/Fix_21110_gliss_text_on_wavy_line

Fix #21110 - text on glissando wavy line