content: Set error{,Code}Style font size to kBaseFontSize, which is 17

Before this, the text was sized by
Theme.of(context).textTheme.bodyMedium.fontSize, thanks to an
AnimatedDefaultTextStyle in the Material widget. That value is 14
when the app's localization state is set to render text as
"English-like" (see [Typography]), which at this point I think it
always is.

lib/widgets/content.dart

@@ -1198,8 +1198,9 @@ InlineSpan _errorUnimplemented(UnimplementedNode node) {
   }
 }
 
-const errorStyle = TextStyle(fontWeight: FontWeight.bold, color: Colors.red);
+const errorStyle = TextStyle(
+  fontSize: kBaseFontSize, fontWeight: FontWeight.bold, color: Colors.red);
 
 final errorCodeStyle = kMonospaceTextStyle
-  .merge(const TextStyle(color: Colors.red))
+  .merge(const TextStyle(fontSize: kBaseFontSize, color: Colors.red))
   .merge(weightVariableTextStyle(null)); // TODO(a11y) pass a BuildContext