This gets rid of the need to pass context to all cursor functions. In
practice context is always immutable when interacting with cursors.
A nicety of this is in the follow-up PR we will be able to implement
Iterator for all Cursors/filter cursors (hell, we may be able to get rid
of filter cursor altogether, as it is just a custom `filter` impl on
iterator trait).
Release Notes:
- N/A
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>