Highlight MR diffs that are too large to be shown

Similar to #16047 (closed), this issue aims to visually emphasize hidden diffs in merge requests, to avoid users missing them altogether, especially when they need to be reviewed.

This case is scoped to diffs that are too large to be shown, and the user must navigate to the file directly to view the changes.

Proposal

Reusing the design proposed in #16047 (closed):

1. Title: Changes are too large to be shown.
2. Button: View file @ {SHA}
3. Background: $orange-50
4. Button variant: Default