What does this add?
===================
This PR adds an extra button to the poll to show the absolute number of
people who voted for each option. This button will only be added for
the single/multi-select bar chart.
Related meta topic: https://meta.discourse.org/t/absolute-numbers-in-polls/32771
* `@ember/owner` instead of `@ember/application`
* `discourse-i18n` instead of `I18n`
* `{ service } from "@ember/service"` instead of `inject as service`
During migration of Poll plugin from widget basis to glimmer, some functionality was inadvertently dropped:
- A single button should appear instead of the dropdown menu when there is only one valid "poll admin" action
- No button should appear when there are no valid "poll admin" actions for current user
This PR restores the original behaviour and adds test coverage (that didn't exist prior to migration, partly why it wasn't caught earlier)
relates to #27204
related meta topic: https://meta.discourse.org/t/what-is-the-gear-button-under-the-poll-for/315477/2
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.
