Search: use chunk match streaming API

Created by: camdencheek

The search backend has recently been migrated to the richer ChunkMatch data type, which is a type that makes it possible to represent multiline matches as one logical match. This has been exposed over the streaming API, and is enabled by the cm query param. When set, the ChunkMatches field will be populated on the EventContentMatch instead of the LineMatches field.

We should migrate the client to use the new streaming API. This will allow us to display the correct number of results when we have multiline results instead of counting each line of the result as a separate match.