Diff View: Scroll to center of hunks when reviewing (#25846)

When reviewing hunks, scroll to put them at the center of the screen
so you can better see the context around that hunk.

The field `center_cursor` was added to the actions `editor::GoToHunk`
and `editor::GoToPrevHunk`, this was set to `false` by default in
keymaps, as it wouldn't help with in-editor navigation.

The field is set to `true` for when you trigger `git::StageAndNext`
and `git::UnstageAndNext`, this is also `true` for the buttons in the
Diff View toolbar.

Release Notes:

- N/A

assets/keymaps/vim.json

@@ -238,8 +238,8 @@
       "] x": "vim::SelectSmallerSyntaxNode",
       "] d": "editor::GoToDiagnostic",
       "[ d": "editor::GoToPrevDiagnostic",
-      "] c": "editor::GoToHunk",
-      "[ c": "editor::GoToPrevHunk",
+      "] c": ["editor::GoToHunk", { "center_cursor": true }],
+      "[ c": ["editor::GoToPrevHunk", { "center_cursor": true }],
       "g c": "vim::PushToggleComments"
     }
   },