While looking into how to implement #4901, noticed that the current
`Goto next/previous diagnostic` behaved a bit weirdly. That is, when
there are multiple errors that have overlapping ranges, only the first
one can be chosen to be active by the `go_to_diagnostic_impl`.

### Previous behavior:


https://github.com/zed-industries/zed/assets/71292737/95897675-f5ee-40e5-869f-0a40066eb8e3

Doesn't go through all the diagnostics, and going backwards and forwards
doesn't show the same diagnostic always.

### New behavior:


https://github.com/zed-industries/zed/assets/71292737/81f7945a-7ad8-4a34-b286-cc2799b10500

Should always go through the diagnostics in a consistent manner.

Release Notes:
* Improved the behavioral consistency of "Go to Next/Previous
Diagnostic"