Merge or-operator matches at the file level

Created by: rvantonder

Currently we merge matches in a query like foo or bar, but at the repo level, not the file level. This means that if a file contains both foo or bar, only one of the two terms are highlighted in the web client.

We can do the merge level at the file level, or convert or expressions to regexp (which will take care of merging at the file level deeper in our search logic). We need both ways to exist to include non-regexp modes (like structural search).