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.
Why this change?
Previously just using the `addToolbarPopupMenuOptionsCallback` plugin
API itself was insufficient because it required the return object to
include an `action` key which only accepted a name of the action
function as a string. This was highly problematic because the action
function had to be defined on the `composer` service which means using
the `modifyClass` API to add the action function. This made the API
awkward to use leading to poor developer experiencec.
What does this change do?
This commit introduces a couple of improvemnts to the API.
1. First the API has been renamed to `addComposerToolbarPopupMenuOption` because
the API no longer accepts a callback function which was quite
redundant. Instead, it now accepts an Object. The
`addToolbarPopupMenuOptionsCallback` API function is deprecated and
will be dropped in Discourse 3.3. Note that passing the API a
function is still supported but will be dropped when the `addToolbarPopupMenuOptionsCallback`
is removed.
2. The `action` key in the Object passed to the function can now be a
function and is passed the `toolbarEvent` object when called.
3. The `condition` on key in the Object passed to the function can now be a
function and is passed the `composer` service when called.
