fix #6535: grace note ties, also articulations & duration fixes

Implemented ties to and from grace notes - underlying support was there, it just needed to be set up correctly.

In the process, I factored out the code that was recently added to find the linked version of a chord (to support tremolo on grace notes) into a new findLinkedChord function.  I leveraged this to get articulations working for grace notes notes as well, and I also use this for grace notes in undoChangeChordRestLen.  This allows the latter function to be used when changing grace note duration rather than setting the duration directly, thus making that operation link-aware and properly undoable (previously, changing grace note duration did not affect linked staves/parts, and undo did work until a subsequent layout).

BTW, do note the code I removed with "#if 0" in edit.cpp.  This appears to be duplicate code for finding a note to tie too - duplicating the code in searchTieNote.  Everything seems to work just fine with this code removed.