chore: Editor 'plugin' -> 'extension'

They've always been called extensions, not sure why the folder was plugins. Part of ongoing spring cleaning

shared/editor/extensions/DateTime.ts

@@ -0,0 +1,60 @@
+import { InputRule } from "prosemirror-inputrules";
+import { Schema } from "prosemirror-model";
+import { EditorState } from "prosemirror-state";
+import {
+  getCurrentDateAsString,
+  getCurrentDateTimeAsString,
+  getCurrentTimeAsString,
+} from "../../utils/date";
+import Extension from "../lib/Extension";
+import { Dispatch, EventType } from "../types";
+
+/**
+ * An editor extension that adds commands to insert the current date and time.
+ */
+export default class DateTime extends Extension {
+  get name() {
+    return "date_time";
+  }
+
+  inputRules() {
+    return [
+      // Note: There is a space at the end of the pattern here otherwise the
+      // /datetime rule can never be matched.
+      // these extra input patterns are needed until the block menu matches
+      // in places other than the start of a line
+      new InputRule(/\/date\s$/, ({ tr }, _match, start, end) => {
+        tr.delete(start, end).insertText(getCurrentDateAsString() + " ");
+        this.editor.events.emit(EventType.blockMenuClose);
+        return tr;
+      }),
+      new InputRule(/\/time\s$/, ({ tr }, _match, start, end) => {
+        tr.delete(start, end).insertText(getCurrentTimeAsString() + " ");
+        this.editor.events.emit(EventType.blockMenuClose);
+        return tr;
+      }),
+      new InputRule(/\/datetime\s$/, ({ tr }, _match, start, end) => {
+        tr.delete(start, end).insertText(`${getCurrentDateTimeAsString()} `);
+        this.editor.events.emit(EventType.blockMenuClose);
+        return tr;
+      }),
+    ];
+  }
+
+  commands(_options: { schema: Schema }) {
+    return {
+      date: () => (state: EditorState, dispatch: Dispatch) => {
+        dispatch(state.tr.insertText(getCurrentDateAsString() + " "));
+        return true;
+      },
+      time: () => (state: EditorState, dispatch: Dispatch) => {
+        dispatch(state.tr.insertText(getCurrentTimeAsString() + " "));
+        return true;
+      },
+      datetime: () => (state: EditorState, dispatch: Dispatch) => {
+        dispatch(state.tr.insertText(getCurrentDateTimeAsString() + " "));
+        return true;
+      },
+    };
+  }
+}