tpl: Fix internal templates usage of safeHTMLAttr

The `safeHTMLAttr` function operates on a full attribute definition, not
just within the attribute value.

Docs: https://gohugo.io/functions/safehtmlattr/

For `opengraph.html`, run the whole `content` HTML attribute through
`safeHTMLAttr`. That will preserve `+` signs in formatted dates.

For `vimeo_simple.html`, `safeHTMLAttr` was in the context of an
attribute value, thus having no effect. In this case we could replace it
with `safeURL`, but since the code is coming from an API it is safer to
just let Go's template engine sanitize the value as it already does with
`provider_url`.

Fixes #5236 (no need to change Go upstream)
Related to #5246

tpl/tplimpl/embedded/templates/shortcodes/vimeo_simple.html

@@ -10,7 +10,7 @@
 {{ $secondClass := "s_video_simple" }}
 <div class="{{ $secondClass }} {{ $class }}">
 {{- with $item }}
-<a href="{{ .provider_url }}{{ .video_id | safeHTMLAttr }}" target="_blank">
+<a href="{{ .provider_url }}{{ .video_id }}" target="_blank">
 {{ $thumb := .thumbnail_url }}
 {{ $original := $thumb | replaceRE "(_.*\\.)" "." }}
 <img src="{{ $thumb }}" srcset="{{ $thumb }} 1x, {{ $original }} 2x" alt="{{ .title }}">