Fix case where line expansion for linked files wants to expand down, but the target line is above the match line

What does this MR do and why?

For #519154 (closed)

There is a very specific error in this scenario:

• An MR with a single file
• Using the Linked File feature
• Linking to a specific line code

In this scenario, the logic for expanding lines eventually resolves to "expand down."
In this specific scenario, however, the correct choice should always be to expand UP.

This is a fix for this scenario (only).

References

• Previous MR: Prevent error when adding line references if th... (!181301 - closed)

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Caveats

• The isExpandDown Linked File computation seems off - a follow-up can simplify the maintainability and readability of this area of the code - perhaps even combining the old logic with the new block. For now, we're just resolving the actual broken UX.