fix(graindoc): Use Markdown bold helper for each case of bolding (gra…

…in-lang#1695)

compiler/graindoc/docblock.re

@@ -116,7 +116,7 @@ let () =
 let title_for_api = (~module_namespace, name) => {
  switch (module_namespace) {
  | Some(module_namespace) =>
- Format.sprintf("%s.**%s**", module_namespace, name)
+ Format.sprintf("%s.%s", module_namespace, Markdown.bold(name))
  | None => name
  };
 };