a11y: Set aria-label for comment action options dropdown
Summary:
Forms should have a label per https://dequeuniversity.com/rules/axe/4.10/link-select.
This is not the case for the `<select>` element above the comment field which has "Add Action..." as its first option which is created via `id(new AphrontFormSelectControl())` in `PhabricatorApplicationTransactionCommentView`. Add an `aria-label` attribute for screenreader use.
Ref T16072
Test Plan:
* While logged in, go to http://phorge.localhost/T1 or http://phorge.localhost/D1 or http://phorge.localhost/P1
* Inspect the `<select>` element above the comment field (which has "Add Action..." as its first option) with and without this patch.
* Optionally, run an Accessibility check in Chromium Lighthouse.
Reviewers: O1 Blessed Committers, chris
Reviewed By: O1 Blessed Committers, chris
Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Maniphest Tasks: T16072
Differential Revision: https://we.phorge.it/D26051