Proof-carrying code: followup improvements

After initial support is landed for PCC (#6090), we can extend it in a bunch of directions:

- [ ] Add PCC flag to fuzzed option set, and resolve any PCC failures (false positives rather than real compiler bugs, hopefully!) as they occur
- [ ] Consider turning on PCC by default in Wasmtime for at least for some configurations (e.g., static memories / no bounds-checking, where it is simplest and least likely to have false positives)
- [ ] Build a "permissive" mode where errors are logged (to `log::warn!`, stderr, or some other side-channel?) without failing compilation; perhaps use this for on-by-default deployment before turning on a strict-enforcing mode
- [ ] Use PCC facts to verify compilation of table accesses
- [ ] Use PCC facts to verify other properties, e.g. invariants of Wasm GC when we have it