(wip): keyed patching for store fields

[gbj]

This builds on top of #4473 to support better patching for keyed store fields. Currently, .patch() works on Vec<_> fields but does an unkeyed list diff: i.e., if you patch vec![0, 1, 2] against vec![2, 1, 0], it will act as if 0 and 2 have both changed values, rather than simply noting that they've been reordered.

This PR adds proper patching for keyed fields by using their key function. Currently it only does this for Vec<_> but this can easily be extended to add support for map types (which are easier) or other collections by implementing the PatchFieldKeyed trait on the collection type.