Add Vim digraphs (#14887)

Vim digraphs are a way to insert special characters using sequences of
two ASCII characters. I've implemented the feature using a new `Digraph`
operator, following the example of `AddSurrounds`. There are still a few
issues that I'm not sure what the best way to resolve them is.

- To insert `ş`, the user must pause between pressing `ctrl-k` and `s
,`, otherwise it triggers the binding for `ctrl-k s`. Is there a way to
disable `ctrl-k *` bindings while in insert, replace or waiting mode?
- Is there a better way to insert a string at all of the cursors? At the
moment I'm constructing the edits manually.
- The table of default digraphs is a 1.4k line rust expression. Is this
okay as long as it's in its own module?
- I'd like a second opinion on how best to structure the settings.json
entry.
- I have omitted the "meta character" feature as I don't think it makes
sense when editing UTF-8 text.

Release Notes:

- Added support for Vim digraphs.

Resolves #11871

assets/keymaps/vim.json

@@ -316,6 +316,7 @@
       "ctrl-u": "editor::DeleteToBeginningOfLine",
       "ctrl-t": "vim::Indent",
       "ctrl-d": "vim::Outdent",
+      "ctrl-k": ["vim::PushOperator", { "Digraph": {} }],
       "ctrl-r": ["vim::PushOperator", "Register"]
     }
   },
@@ -325,6 +326,7 @@
       "escape": "vim::NormalBefore",
       "ctrl-c": "vim::NormalBefore",
       "ctrl-[": "vim::NormalBefore",
+      "ctrl-k": ["vim::PushOperator", { "Digraph": {} }],
       "backspace": "vim::UndoReplace",
       "tab": "vim::Tab",
       "enter": "vim::Enter"
@@ -337,7 +339,8 @@
       "enter": "vim::Enter",
       "escape": "vim::ClearOperators",
       "ctrl-c": "vim::ClearOperators",
-      "ctrl-[": "vim::ClearOperators"
+      "ctrl-[": "vim::ClearOperators",
+      "ctrl-k": ["vim::PushOperator", { "Digraph": {} }]
     }
   },
   {

assets/settings/default.json

@@ -922,7 +922,8 @@
   "vim": {
     "use_system_clipboard": "always",
     "use_multiline_find": false,
-    "use_smartcase_find": false
+    "use_smartcase_find": false,
+    "custom_digraphs": {}
   },
   // The server to connect to. If the environment variable
   // ZED_SERVER_URL is set, it will override this setting.