Add sample vim extension

sample-extensions/package.json

@@ -0,0 +1,5 @@
+{
+  "dependencies": {
+    "monaco-vim": "^0.4.1"
+  }
+}

sample-extensions/vim.js

@@ -0,0 +1,34 @@
+//To use this extension:
+//  copy this file to the userData dir as in https://dyalog.github.io/ride/4.5/customising_your_session:
+//  (package.json and package-lock.json are there for reference)
+//   - Linux: `$HOME/.config/Ride-<version>`
+//   - macOS: `$HOME/Library/Application Support/Ride-<version>` (hidden directory – access from the command line)
+//   - Microsoft Windows: `%APPDATA%\Ride-<version>`
+//  npm install --prefix /dir/to/this/file monaco-vim
+//  export RIDE_JS=/path/to/this/file.js
+//before starting RIDE.
+$.extend(D.commands, {
+  VIM(me) {
+    amdRequire(
+      [ "vs/editor/editor.main",
+        D.el.app.getPath("userData") + "/node_modules/monaco-vim/dist/monaco-vim", ],
+      function (a, MonacoVim) { vimMode = MonacoVim.initVimMode(me, document.createElement("div")); },
+    );
+    me.updateOptions({ lineNumbers: "relative" });
+  },
+  MIV() { vimMode.dispose(); },
+});
+D.remDefaultMap = (me) => { // hijack to run additional code on startup
+  const kbs = me._standaloneKeybindingService;
+  kbs.addDynamicKeybinding( "-editor.action.insertCursorAtEndOfEachLineSelected", null, () => {}, );
+  kbs.addDynamicKeybinding("-editor.action.blockComment", null, () => {});
+  kbs.addDynamicKeybinding("-editor.action.formatDocument", null, () => {});
+  D.commands.VIM(me);
+};
+$.extend(D.Ed.prototype, {
+  setLN(x) { // update the display of line numbers and the state of the "[...]" button
+    const ed = this;
+    ed.me.updateOptions({ lineNumbers: "relative" });
+    ed.dom.querySelector(".tb_LN").classList.toggle("pressed", !!x);
+  },
+});