feat: allow codeblock plaintext inside codeblock and nested lists markdown (#2930)

* fix crash when editing message with empty trailing heading

* remove unused imports

* allow codeblock plaintext inside codeblock by extending fence count

* allow nested list in markdown

src/app/styles/CustomHtml.css.ts

@@ -120,12 +120,23 @@ export const CodeBlockBottomShadow = style({
   background: `linear-gradient(to top, #00000022, #00000000)`,
 });
 
+const BaseList = style({});
 export const List = style([
+  BaseList,
   DefaultReset,
   MarginSpaced,
   {
     padding: `0 ${config.space.S100}`,
     paddingLeft: config.space.S600,
+    selectors: {
+      '& &': {
+        marginTop: config.space.S200,
+        marginBottom: config.space.S200,
+      },
+      'li:last-child &': {
+        marginBottom: 0,
+      },
+    },
   },
 ]);