Web: Truncate and show banner on large location result sets.

Created by: efritz

Related to the effort to improve pagination for LSIF references: https://github.com/sourcegraph/sourcegraph/pull/8778

In the spirit of being transparent about precision and completeness of results, we should probably display a banner when we have more precise results than we are able to show. We must apply a limit on the number of references we'll show for a symbol (momentjs/moment will crash the UI with too many DOM elements displaying 16k unique location references in its own LSIF dump). We should also inform the user that we have more references than what we are able to display (these results are available via the GraphQL API, but we can't show them all at once).

Eventually we should be able to display a link to a reference result set that is filterable based on file, repo, context, etc. This will require eventual integration into the search path and is not currently on any near-term roadmap.