chore: Move editor into codebase (#2930)

shared/editor/commands/backspaceToParagraph.ts

@@ -0,0 +1,26 @@
+import { NodeType } from "prosemirror-model";
+import { EditorState, Transaction } from "prosemirror-state";
+
+export default function backspaceToParagraph(type: NodeType) {
+  return (state: EditorState, dispatch: (tr: Transaction) => void) => {
+    const { $from, from, to, empty } = state.selection;
+
+    // if the selection has anything in it then use standard delete behavior
+    if (!empty) return null;
+
+    // check we're in a matching node
+    if ($from.parent.type !== type) return null;
+
+    // check if we're at the beginning of the heading
+    const $pos = state.doc.resolve(from - 1);
+    if ($pos.parent === $from.parent) return null;
+
+    // okay, replace it with a paragraph
+    dispatch(
+      state.tr
+        .setBlockType(from, to, type.schema.nodes.paragraph)
+        .scrollIntoView()
+    );
+    return true;
+  };
+}