MIDI export: apply accent- and marcato-based compound articulations

[hashimh4]

Resolves: #31432

Accent-staccato, accent-tenuto, marcato-staccato and marcato-tenuto were missing from s_builtInArticulationsValues, so MIDI export applied neither their shortening nor their velocity change, although MuseScore plays them correctly. The values follow the decomposition in ARTICULATION_ABOVE_SPLIT_GROUPS. Scores that store an instrument articulation list resolve through it as before and are unaffected.

Built in CI; I tested the resulting Windows build against the score attached to the issue, and its export before the fix is byte-identical to the reporter's own.

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