MuseSampler: fixed potential compatibility issues

[RomanPudashkin]

Rely only on the museUID, as it remains consistent across versions

[iamtesch]

I believe this should work to keep instruments consistent. Have we tested by:

1. Create a score with an instrument
2. Close MuseScore
3. Update to a new version of the instrument with changed category/vendor names
4. Reopen MuseScore
5. Ensure the instrument still plays back
6. One other thing to check here -- if you expand the list in the mixer does this instrument still show up as "checked" under the new position?

If this is all good, it seems like a reasonable change to me.

[iamtesch]

I think step "6" may be the one that doesn't work here, because the AudioResourceMeta object still has the old values in it. I don't have enough familiarity with the MuseScore code around the ISynthesizerPtr to have an idea of all the side effects here, but I think originally the findInstrument code was an exact match to eliminate the possibility of the data in AudioResourceMeta being a mismatch with the instrument loaded from the sampler.

Do we need to rewrite the data here stored in the score somehow with the updated values?

[RomanPudashkin]

If we renamed the instrument category, we could indeed have a problem with the mixer menu. Because both the category and the name were part of the resource ID. Now they are not, and we will always use the museUID as the resource ID instead. We will also convert the old ID format to the new one when reading the score. Thus, all checks like resourceMeta1.id == resourceMeta2.id should work fine even if we change the category or name

[iamtesch]

Looks good to me! Thanks :D