## Problem
Previously, we were using `observe_closure_duration` in `VirtualFile`
file opening code, but this doesn't support async open operations, which
we want to use as part of #4743.
## Summary of changes
* Move the duration measurement from the `with_file` macro into a
`observe_duration` macro.
* Some smaller drive-by fixes to replace the old strings with the new
variant names introduced by #5273
Part of #4743, follow-up of #5247.
a18d6d9ae3