Blob refactor: Show correct control buttons when viewing a blob

What does this MR do and why?

This MR ensures that the correct control buttons are rendered when viewing a blob in the refactored blob viewer.

Note, changes in this MR are behind the :refactor_blob_viewer feature flag.

Screenshots or screen recordings

before	after

How to set up and validate locally

Enable the Blob Viewer Refactor feature flag

Feature.enable(:refactor_blob_viewer)

Open a source file

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #348304 (closed)