At its core, this commit changes `OpaqueProperties` (aka a void*) to
`PropertyRef`, which is a {TypeID, void*}, where the TypeID is the ID of
the storage type of the given property (which can, as is often the case
for operations, be a struct of other properties).
Long-term, this change will allow for
1) Some sort of getFooPropertyRef() on property structs, allowing
individual members to be extracted generically
2) By having a property kind that is an OwningProprtyRef, generic
parsing (in combination with a bunch of other changes) 3) Probably a
safer C/Python API because we'll be able to indicate what's supposed to
be under a given void*
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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>