Fix searching for files by path

What does this MR do?

Modifies Gitlab::FileFinder to return Gitlab::SearchResult::FoundBlob results for blobs found by filename

Are there points in the code the reviewer needs to double check?

We're pulling the actual blob contents from disc where previously we wouldn't. I'm using a batch call to do so, and limiting the size of the returned data, but do I need to be more restrictive here?

Why was this MR needed?

Searching is broken in some cases

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes #36939 (closed)