Support hunk-wise StageAndNext and UnstageAndNext (#25845)

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

crates/gpui/src/action.rs

@@ -399,6 +399,8 @@ macro_rules! action_with_deprecated_aliases {
 /// Registers the action and implements the Action trait for any struct that implements Clone,
 /// Default, PartialEq, serde_deserialize::Deserialize, and schemars::JsonSchema.
 ///
+/// Similar to `actions!`, but accepts structs with fields.
+///
 /// Fields and variants that don't make sense for user configuration should be annotated with
 /// #[serde(skip)].
 #[macro_export]