[mod] result templates: move iframe to macro and fix page rendering for non-YouTube links (#5960)

This PR moves the `iframe` logic into a macro, so that `videos.html` and `general.html` both can benefit from the workaround to fix YouTube results by @return42 in https://github.com/searxng/searxng/pull/5858

It also fixes that only YouTube videos contained the closing `>` after `<iframe border="0" ...`, the regression has been caused by https://github.com/searxng/searxng/pull/5858

## Why is this change important?

Currently, the page breaks if there's any non-YouTube Iframe

Here, the page ends in the middle of the results and the footer and page number selector are not visible.

searx/templates/simple/macros.html

@@ -67,3 +67,13 @@
          class="checkbox-onoff"{{- ' ' -}}
          {%- if checked -%} checked{%- endif -%}/>
 {%- endmacro -%}
+
+<!-- iframe that additionally sets some extra feature attrs for videos -->
+{%- macro iframe(iframe_src) -%}
+  <iframe data-src="{{iframe_src}}" frameborder="0" allowfullscreen
+    {% if result.parsed_url.hostname in ("www.youtube.com", ) -%}
+    allow="picture-in-picture" referrerpolicy="origin"
+    {%- endif -%}
+    >
+  </iframe>
+{%- endmacro -%}