Mention Multimesh custom data will be compressed to half in Compatibility

[jsjtxietian]

For #93875

[Mickeon]

If you "Note" it should be put into a [b]Note[/b] like many messages of this nature.
Also may be worth documenting in more places other than this one setter (such as the corresponding getter, but there are likely more)

[Mickeon]

This is nice as is, but I still stand by:

Also may be worth documenting in more places other than this one setter (such as the corresponding getter, but there are likely more)

[Lielay9]

I'd copy the note for instance-color too. It could also be mentioned in the buffer, but since it has no description atm, it's not as important.

[akien-mga]

Thanks!