Offer single file mode when Rapid Diffs hit limits

Everyone can contribute. Help move this issue forward while earning points, leveling up and collecting rewards.

• Close this issue

When we render Rapid Diffs we might hit diff limits. Either limited by the number of files, total visible lines or bytesize. When that happens we stop rendering diff contents and only show diff files with placeholders:

This is not very useful for the reviewer. To improve that experience we could:

1. Stop rendering files with placeholders when diff limits are hit (this will improve page's performance for non-limited files). Instead, show a 'Continue in a single file mode' button. The button will switch the whole page to a single file mode and open the next collapsed file in an uncollapsed state. All the further navigations will always show uncollapsed files. The single file mode setting should not be persisted for other pages.
2. Add 'Switch to single file mode' to the overflow warning before the diffs, so we can enter this mode sooner.
3. Show a separator in the file browser tree when we reach the limits threshold. This will give user an understanding how many files he/she can actually see before having to switch into a single file mode.

Example how this could look like:

Page start	Page end