vim: Add more diff stuff (#17456)

Release Notes:

- vim: Added `:diff` and `:revert` (that work with `'<,'>`) to open the
selected diff and revert it.
- vim: Added `d o` to open the diff and `d p` to revert (spiritually
similar to vim's do/dp, though obviously not the same)
- vim: Added `ctrl-p` and `ctrl-n` to summon the autocomplete menu in
insert mode.

assets/keymaps/vim.json

@@ -323,6 +323,8 @@
       "ctrl-t": "vim::Indent",
       "ctrl-d": "vim::Outdent",
       "ctrl-k": ["vim::PushOperator", { "Digraph": {} }],
+      "ctrl-p": "editor::ShowCompletions",
+      "ctrl-n": "editor::ShowCompletions",
       "ctrl-r": ["vim::PushOperator", "Register"]
     }
   },
@@ -394,7 +396,9 @@
     "context": "vim_operator == d",
     "bindings": {
       "d": "vim::CurrentLine",
-      "s": ["vim::PushOperator", "DeleteSurrounds"]
+      "s": ["vim::PushOperator", "DeleteSurrounds"],
+      "o": "editor::ToggleHunkDiff", // "d o"
+      "p": "editor::RevertSelectedHunks" // "d p"
     }
   },
   {