Fix #283964 - Linked parts for single voices don't work

[njvdberg]

Resolves: https://musescore.org/en/node/283964

Corrects recognition of linked staves with a part and linked staves over excerpts.

Score::undoAddCR() will find all linked staves for the passed ChordRest and iterates over all these staves and decides what to do. The root cause of this issue was this algorithm didn't clearly distinguish between the two different kind of linked staves:

• 1 Linked staves within a part

• 2 Linked staves between master score and scores on excerpt.
  This PR now handles creating a ChordRest for the following cases:

• 1 On non-linked staff at the master score.

• 2 On a staff linked, via an excerpt, to another score on another part.

• 3 On a staff linked, via an excerpt, to another score on another part using the voice-to-part feature.

• 4 On a staff linked to another staff on the same score ("linked staves" in the Parts dialog).

• 5 On a staff linked to another staff on the same score and to another part.

• 6 On a staff linked to another staff on the same score and to another part using the voice-to-part.
  All 6 cases are tested by creating a ChordRest on the master score and all, if applicable, on any of the linked staves.

Corrects recognition of linked staves with a part and linked staves over excerpts.

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[njvdberg]

This PR is related to, but not the same as PR #6116. Both are solving another issues with linked staffs.