Resolve "Can't create a merge request containing a binary file with non-UTF-8 characters"

What does this MR do?

Fixes the case where a binary file in an MR diff contains byte sequences that aren't expressible in UTF-8.

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

I wish I could use add_column_with_default, but this needs to be in a patch release, so the migration has to be quick. The packing is the same as Psych's, so that we are compatible with our old diffs when we migrate them, too.

Why was this MR needed?

Some files prevent an MR diff from being created. PDFs created from Illustrator seem to be particularly prone to this.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #35539 (closed).