This PR adds the `whole_excerpt` field to the actions:

- `git::StageAndNext`
- `git::UnstageAndNext`

Which is set by false by default, effectively, now staging and unstaging
with these actions is done hunk-by-hunk, this also affects the `Stage`
and
`Unstage` buttons in the Diff View toolbar.

A caveat: with this PR, there is no way to configure the buttons in the
Diff
View toolbar to restore the previous behavior, if we want, I think we
can make
it a setting, but let's see if anyone really wants that.

Release Notes:

- N/A