Bends: change implemention of bend steps to "note-to-note" (not sp.)

OS: Windows 10 (10.0), Arch.: x86_64, MuseScore version (64-bit): 3.1.0.6041, revision: 5b23862

Currently, the length of a bend is restricted, and, unlike lines or slurs, bends cannot stretch with the score. Autoplacement can make things worse because it forces the bend onto just one note, when in reality it may need to extend over several notes. As a result you can get large gaps in the score: e.g.

Solution: In the Bend properties window, each added node should extend the bend to the next note. The bend should now extend and contract naturally with the notes of the score, just like slurs and lines.

Related to #286108: [EPIC] Bends issues.