Unite all of the melody/sound string representations

Across pxt-common-packages and pxt-microbit, we currently have four different ways of representing sounds/melodies

1. The MicroPython format of arrays of strings (detailed here)
2. The melody format used in pxt-arcade (detailed here)
3. The SoundExpression string format used by microbit-codal (detailed here)
4. The simplified melody format used by the playMelody block

None of these formats are compatible/interchangeable and there is a lot of overlap between them. It would be nice to come up with one format to rule them all, so to speak. I believe the requirements look something like this

1. Ability to specify a string of note/octave/duration in a human readable way
2. Ability to specify a custom sound/instrument with:
   a. Waveform
   b. Envelopes for different parameters (e.g. pitch, volume)
   c. Duration
   d. Effects (e.g. interpolation curves, tremolo/vibrato)
   e. Chains of all of the above (e.g. multipart sounds to simulate complex envelopes like ADSR)

Start by comparing the existing melody and sound representations across pxt-common-packages and pxt-microbit, using the linked MicroPython, pxt-arcade, and SoundExpression format documentation. Determine whether a unified format can cover the listed note, waveform, envelope, duration, effect, and chaining requirements; done requires an agreed design rather than a single localized code change.