We are going to use this in the multi-buffer to produce a summary for an
`Excerpt` that contains a `Range<Anchor>`.
Release Notes:
- N/A
Co-authored-by: Nathan <nathan@zed.dev>
This lets us provide a context when constructing the zero value. We need
it so we can require anchors to be associated with a buffer id, which
we're doing as part of simplifying the multibuffer API.
Release Notes:
- N/A
Co-authored-by: Nathan <nathan@zed.dev>
