Searcher: return LineOffset in LineMatch
Created by: camdencheek
This adds LineOffset to the LineMatch in the searcher response. This allows us to calculate the byte offset of the the offsets and lengths so we can unify LineColumn and Location (this is the last place missing that information).
This change will be ephemeral since I plan to get rid of LineMatch
from the
searcher API in replacement of a hunk-based type, but for now this lets
me move forward incrementally.
Stacked on #36114
Test plan
Updated tests, but it's not actually used yet. Will do so in the followup PR.