add H3 to editor formatting toolbar (#6791)

app/editor/menus/formatting.tsx

@@ -16,6 +16,7 @@ import {
   OutdentIcon,
   IndentIcon,
   CopyIcon,
+  Heading3Icon,
 } from "outline-icons";
 import { EditorState } from "prosemirror-state";
 import { isInTable } from "prosemirror-tables";
@@ -107,6 +108,14 @@ export default function formattingMenuItems(
       attrs: { level: 2 },
       visible: allowBlocks && !isCode,
     },
+    {
+      name: "heading",
+      tooltip: dictionary.subheading,
+      icon: <Heading3Icon />,
+      active: isNodeActive(schema.nodes.heading, { level: 3 }),
+      attrs: { level: 3 },
+      visible: allowBlocks && !isCode,
+    },
     {
       name: "blockquote",
       tooltip: dictionary.quote,