fix #287047, fix #290968: update mmrest bbox including the number

[ecstrema]

Resolves: https://musescore.org/en/node/287047 (first part) and https://musescore.org/en/node/290968

sorry for the bad quality gif

second commit fixes hardcoded values that were not working properly with special staves. There is no link in the issue tracker for that as i rescolved the bug when i discovered it.
Steps to reproduce for those curious:

1. new score with one instrument: triangle (or any single lined staff)
2. press "M" to switch to MMRests.
3. move number down: the collision detection doesn't work properly.

Result after the second commit

• I signed CLA
• I made sure the code in the PR follows the coding rules
• I made sure the code compiles on my machine
• I made sure there are no unnecessary changes in the code
• I made sure the title of the PR reflects the core meaning of the issue you are solving
• I made sure the commit message(s) contain a description and answer the question "Why do those changes fix that particular issue?" or "Why are those changes really necessary as improvements?"
• I made sure the commit message title starts with "fix #424242:" if there is a related issue
• [n/a] I created the test (mtest, vtest, script test) to verify the changes I made

[Jojo-Schmitz]

Make sure the commit titles contain that 'fix #nnnnn', you ticked that box but didn't obey to it ;-)

[anatoly-os]

@IsaacWeiss this PR cannot be easily merged to master due to the changes you've made. Could you please take a look at this PR and extract the changes we still need and make the PR to master?

[IsaacWeiss]

No need, equivalent changes were included in #6211.