QQmlSA: better support for analyzing function calls

qmllint/QQmlSA currently only can analyze function calls via onRead. That's needlessly expensive if you only care about calls (check runs too often), and also makes it needlessly hard to write such checks.

One problematic aspect is that it's not possible to trace functions that were stored in variables, but that's generally unfeasible, and can be ignored.a

We should provide public API for this use case at the QQmlSA level. Whether this would become a new pass type or an extension of the ProperyPass API has to be investigated.