feat: migrate cpp/language/basic_concepts/definition (#83)

* feat: migrate cpp/language/basic_concepts/definition

* feat: add component `Incomplete`

* feat: update docs for `Incomplete`

* fix: correct links in cpp/language/basic_concepts/definition

* fix: emphasize undefined behavior

Author: Sudrut

src/components/Incomplete.astro

@@ -0,0 +1,13 @@
+---
+import { Aside } from "@astrojs/starlight/components";
+
+interface Props {
+  reason: string;
+}
+
+const { reason } = Astro.props;
+---
+
+<Aside title="This section is incomplete">
+  Reason: {reason}
+</Aside>

src/components/index.ts

@@ -13,6 +13,7 @@ import { DR, DRList } from "@components/defect-report";
 import { Revision, RevisionBlock } from "@components/revision";
 import AutoCollapse from "@components/AutoCollapse.astro";
 import FlexTable from "@components/FlexTable.astro";
+import Incomplete from "@components/Incomplete.astro";
 import WG21PaperLink from "@components/WG21PaperLink.astro";
 
 export {
@@ -35,5 +36,6 @@ export {
   RevisionBlock,
   AutoCollapse,
   FlexTable,
+  Incomplete,
   WG21PaperLink,
 };