fix(search): avoid missing spaces between paragraphs in search results (#2199)

- Use a common post-snippet for search results to avoid line break issues
- Reduce Jekyll include files to speed up the build
- Remove outdated key from search.json

_includes/search-loader.html

@@ -12,7 +12,7 @@
         {tags}
       </div>
     </header>
-    <p>{snippet}</p>
+    <p>{content}</p>
   </article>
 {% endcapture %}