Fix tremolo articulation mapping for individual string instruments

    - Add missing tremolo articulation mappings to individual VIOLIN, VIOLA, VIOLONCELLO, and CONTRABASS
    - Previously only *_SECTION variants had tremolo mappings, causing tremolo to fall back to default arco sound
    - Individual instruments now correctly map tremolo to program 44 on their respective banks (20, 30, 40, 50)
    - Fixes issue #21122: Multichannel instruments don't select correct midi preset for tremolo on SF2 fonts

    Affected mappings:
    - VIOLIN: Added Tremolo8th/16th/32nd/64th → midi::Program(20, 44)
    - VIOLA: Added Tremolo8th/16th/32nd/64th → midi::Program(30, 44)
    - VIOLONCELLO: Added Tremolo8th/16th/32nd/64th → midi::Program(40, 44)
    - CONTRABASS: Added Tremolo8th/16th/32nd/64th → midi::Program(50, 44)

    Now string instruments (violin, viola, violoncello, contrabass) correctly select tremolo MIDI presets when using SF2 soundfonts.

    Changes made:

    1. Updated soundmapping.h:
       - Added missing tremolo articulation mappings for individual instruments
       - VIOLIN: Bank 20, Program 44
       - VIOLA: Bank 30, Program 44
       - VIOLONCELLO: Bank 40, Program 44
       - CONTRABASS: Bank 50, Program 44

    Fixes: #21122

Author: manolo

src/framework/audio/engine/internal/synthesizers/fluidsynth/soundmapping.h

@@ -923,7 +923,11 @@ inline const ArticulationMapping& articulationSounds(const mpe::PlaybackSetupDat
         { mpe::ArticulationType::SnapPizzicato, midi::Program(20, 45) },
         { mpe::ArticulationType::Pizzicato, midi::Program(20, 45) },
         { mpe::ArticulationType::PalmMute, midi::Program(20, 45) },
-        { mpe::ArticulationType::Mute, midi::Program(20, 40) }
+        { mpe::ArticulationType::Mute, midi::Program(20, 40) },
+        { mpe::ArticulationType::Tremolo8th, midi::Program(20, 44) },
+        { mpe::ArticulationType::Tremolo16th, midi::Program(20, 44) },
+        { mpe::ArticulationType::Tremolo32nd, midi::Program(20, 44) },
+        { mpe::ArticulationType::Tremolo64th, midi::Program(20, 44) },
     };
 
     static const ArticulationMapping VIOLA_SECTION = {
@@ -941,7 +945,11 @@ inline const ArticulationMapping& articulationSounds(const mpe::PlaybackSetupDat
         { mpe::ArticulationType::SnapPizzicato, midi::Program(30, 45) },
         { mpe::ArticulationType::Pizzicato, midi::Program(30, 45) },
         { mpe::ArticulationType::PalmMute, midi::Program(30, 45) },
-        { mpe::ArticulationType::Mute, midi::Program(30, 41) }
+        { mpe::ArticulationType::Mute, midi::Program(30, 41) },
+        { mpe::ArticulationType::Tremolo8th, midi::Program(30, 44) },
+        { mpe::ArticulationType::Tremolo16th, midi::Program(30, 44) },
+        { mpe::ArticulationType::Tremolo32nd, midi::Program(30, 44) },
+        { mpe::ArticulationType::Tremolo64th, midi::Program(30, 44) },
     };
 
     static const ArticulationMapping VIOLONCELLO_SECTION = {
@@ -959,7 +967,11 @@ inline const ArticulationMapping& articulationSounds(const mpe::PlaybackSetupDat
         { mpe::ArticulationType::SnapPizzicato, midi::Program(40, 45) },
         { mpe::ArticulationType::Pizzicato, midi::Program(40, 45) },
         { mpe::ArticulationType::PalmMute, midi::Program(40, 45) },
-        { mpe::ArticulationType::Mute, midi::Program(40, 49) }
+        { mpe::ArticulationType::Mute, midi::Program(40, 49) },
+        { mpe::ArticulationType::Tremolo8th, midi::Program(40, 44) },
+        { mpe::ArticulationType::Tremolo16th, midi::Program(40, 44) },
+        { mpe::ArticulationType::Tremolo32nd, midi::Program(40, 44) },
+        { mpe::ArticulationType::Tremolo64th, midi::Program(40, 44) },
     };
 
     static const ArticulationMapping CONTRABASS_SECTION = {
@@ -978,6 +990,10 @@ inline const ArticulationMapping& articulationSounds(const mpe::PlaybackSetupDat
         { mpe::ArticulationType::Pizzicato, midi::Program(50, 45) },
         { mpe::ArticulationType::PalmMute, midi::Program(50, 45) },
         { mpe::ArticulationType::Mute, midi::Program(50, 43) },
+        { mpe::ArticulationType::Tremolo8th, midi::Program(50, 44) },
+        { mpe::ArticulationType::Tremolo16th, midi::Program(50, 44) },
+        { mpe::ArticulationType::Tremolo32nd, midi::Program(50, 44) },
+        { mpe::ArticulationType::Tremolo64th, midi::Program(50, 44) },
     };
 
     static const ArticulationMapping BRASS = {