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

assets/keymaps/default-linux.json

@@ -370,8 +370,8 @@
       "ctrl-shift-v": "markdown::OpenPreview",
       "ctrl-alt-shift-c": "editor::DisplayCursorNames",
       "ctrl-alt-y": "git::ToggleStaged",
-      "alt-y": "git::StageAndNext",
-      "alt-shift-y": "git::UnstageAndNext",
+      "alt-y": ["git::StageAndNext", { "whole_excerpt": false }],
+      "alt-shift-y": ["git::UnstageAndNext", { "whole_excerpt": false }],
       "alt-.": "editor::GoToHunk",
       "alt-,": "editor::GoToPrevHunk"
     }