The "migration to Glimmer" has been broken out here from #27155 to make the review process less onerous and reduce change risk:
* DEV: migrates most of the widget code to Glimmer in prep for IRV additions
* NB This already incorporates significant amounts of review and feedback from the prior PR.
* NB because there was significant additional feedback relating to older Poll code that I've improved with feedback, there are some additional changes here that are general improvements to the plugin and not specific to IRV nor Glimmer!
* There should be no trace of IRV code here.
Once this is finalised and merged we can continue to progress with #27155.
Adds an optional title attribute to polls. The rationale for this addition is that polls themselves didn't contain context/question and relied on post body to explain them. That context wasn't always obvious (e.g. when there are multiple polls in a single post) or available (e.g. when you display the poll breakdown - you see the answers, but not the question)
As a side note, here's a word on how the poll plugin works:
> We have a markdown poll renderer, which we use in the builder UI and the composer preview, but… when you submit a post, raw markdown is cooked into html (twice), then we extract data from the generated html and save it to the database. When it's render time, we first display the cooked html poll, and then extract some data from that html, get the data from the post's JSON (and identify that poll using the extracted html stuff) to then render the poll using widgets and the JSON data.
This required properly plumbing the guardian into the serializer.
Notably, the default state in the client was not changed - if you haven't voted in
the poll, you need to click the button to view the results instead of the results
being immediately visible on page load.
Implements https://meta.discourse.org/t/-/138108
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
