search: gate and/or query execution
Created by: rvantonder
Stacked on #9827.
This PR:
- disables and/or queries in literal search mode (as planned in RFC 94)
- uses a cheap heuristic to fall back to the existing older parser if possible. It's not critical that this heuristic fires (it's OK if it's not 100% accurate). The intent is to help a gradual transition away from something that has been in use for longer than the new code.