wasm: optimize with handling in planner

[srenatus]

Right now, any encountered with statement will cause all data functions to be put aside, and replanned (in a new "generation"):

opa/internal/planner/planner.go

Lines 611 to 620 in 30a0654

	// If any of the with statements targeted the data document we shadow
	// the existing planned functions during expression planning. This
	// causes the planner to re-plan any rules that may be required during
	// planning of this expression (transitively).
	if len(dataRefs) > 0 {
	p.funcs.Push(map[string]string{})
	for _, ref := range dataRefs {
	p.rules.Push(ref)
	}
	}

We could attempt to be more sophisticated here. In bundles with heavy with usage, this causes the wasm code to have a whole lot of functions.