[MU4 Issue] Tempo change lines not mapping correctly after MusicXML import

[bkunda]

Describe the bug Importing MusicXML files with tempo change lines from Sibelius and Dorico produces incorrect results in MS4.

MusicXML from Sibelius:

• "Accel." and "Rit." lines are rendered in MS4 as staff text with no playback properties

https://user-images.githubusercontent.com/86290556/175502721-fd2aeb66-e113-4f90-9f47-dba375329756.mp4

MusicXML from Dorico:

• "Accel." and Rit." lines also render as staff text, but they come with a multitude of hidden tempo change text elements (all stacked on top of one another).
• Playback doesn't work

To Reproduce Steps to reproduce the behavior:

1. Create a score in Sibelius/Dorico with "accel." and "rit." lines
2. Export the file in the .musicxml format
3. Open the file in MS4.

Expected behavior Ideally, "accel." and "rit." lines (and all other conceivable tempo change lines) from Sibelius and Dorico would map to gradual tempo change lines in MS4 with the correct default change values for each line type (I.e. "accel.", "rit.", "rall.", "allarg.", etc.).

This behaviour is apparently a key workflow requirement for MuseClass.

Platform information

• MacOS 12.3.1 (M1)

Example files for testing tempo-changes-xml-test.zip Flows from test-tempochanges-dorico.zip