Add dirty indicator to Breadcrumbs

[Qkessler]

Change Summary

Users commonly remove the Tab Bar to remove noise while they write/code. I do it myself. Nevertheless, there's a gap in visibility over the current pane when one disables the tab bar: we miss the dirty indicator on the current pane. When I change something without saving, there's no visual indicator that the pane was changed, leading to potential mistakes.

With this PR, I propose using the Breadcrumbs for that. It commonly includes the buffer/file name, even if the outline doesn't show an inner element. By adding the indicator on the Breadcrumbs, we ensure people who choose to remove the tab bar still have the visibility while maintaining the display minimal.

I'm open to adding this behind a configuration flag. I'd even be good for both the tab bar and the breadcrumbs to share that configuration option, to avoid duplication.

Closes #22390

Risks associated with this change

This change introduces a different usage of the Breadcrumbs. I see little risk, considering using the left of the breadcrumbs is non-obstrusive.

Testing

To test it, I made the changes and spawn a Zed instance with RUST_LOG=debug scripts/zed-local -1. Here's what the pane looks like without the change:

and here's what it looks after, whenever I make a change on the file and don't save:

Release Notes:

• Added file change Indicator on Breadcrumbs

[Qkessler]

@danilo-leal , interested in your thoughts for this change. Let me know what you think coming from the UX perspective.

[0x2CA]

Thank you for your work, there is an indicator that is very good, but it will cause the original text to move to the right as a whole, is this appropriate? I think using color markers to mark the path would be better, wouldn't it?

[bonniesimon]

I have a few suggestions:

Have the marker on the right side (This is what VsCode does):

Have the marker at the end of the breadcrumbs:

[Qkessler]

Thanks both for the suggestions, great ones. Interested in hearing from @danilo-leal , who has context on the direction for Zed's design.