wasm: only shadow ruletrie with matching data refs

[srenatus]

Before, the planner had decided to shadow all rules whenever a with statement was targeting "data".
Now, it's looking at the ruletrie to see if whatever ref the with statement targets actually is a rule (or package ref). If so, it'll shadow, if not, it won't.

Fixes #3150.

---

So, for one of the bundles I've been testing this with, it helped a lot:

• Function count: 1102 -> 816
• module size: 700K -> 516K

In that bundle, there's not been ANY func gen increase, so, no with statement was targeting a virtual rule. It also means that the mapping data we're using for #3058 has become a lot smaller, from

g0:
   foo:
     bar: 10
     baz: 11
g1:
  foo:
    bar: 12
    baz: 13
...
g78:
  foo:
    ...

to only the g0 subtree.

[tsandall]

LGTM