Add first-party support for Crowdsignal poll/survey oEmbeds

[westonruter]

Related: #1925.

• Promotes WPCOM_AMP_Polldaddy_Embed to AMP_Crowdsignal_Embed_Handler.
• Implements support for the Crowdsignal rebrand from PollDaddy.
• Removes shortcode handling from the AMP plugin since it is Jetpack-specific. See Add AMP support for shortcodes and oEmbeds for Crowdsignal (Polldaddy) Automattic/jetpack#11484 for where the code is moved to.

• Ensure that Add AMP support for shortcodes and oEmbeds for Crowdsignal (Polldaddy) Automattic/jetpack#11484 has been released in a stable version.

[kraftbj]

Confirming that since Crowdsignal/Polldaddy is a core oembed, those embeds will work in some decent way without Jetpack in AMP after this PR?

[westonruter]

@kraftbj oh, I wasn't aware that it is a core embed now. Well, without support the support of the AMP plugin or Jetpack then the sample content from Automattic/jetpack#11484 gets rendered as:

In other words, the poll oEmbed successfully gets a fallback since it has noscript for the AMP plugin to unwrap. The script does cause a validation error which the AMP plugin catches:

The Survey oEmbed, however, renders nothing since the oEmbed response is only a script:

<script type="text/javascript">(function(d,c,j){if(!document.getElementById(j)){var pd=d.createElement(c),s;pd.id=j;pd.src=('https:'==document.location.protocol)?'https://polldaddy.com/survey.js':'http://i0.poll.fm/survey.js';s=document.getElementsByTagName(c)[0];s.parentNode.insertBefore(pd,s);}}(document,'script','pd-embed'));</script>

This lack of noscript seems like a shortcoming of the Crowdsignal survey oEmbed response.

Nevertheless, now that Crowdsignal is actually directly supported by core, it seems actually that it shouldn't be removed. More specifically, the oEmbed handling shouldn't be removed. The shortcode handling, however, is something that should be handled rather by the Jetpack or Crowdsignal plugins since the shortcodes are not defined in core. Agree?

[amedina]

LGTMT