This lays the groundwork for converting SelectKit subclasses to native class syntax. This commit is designed to be entirely backwards-compatible, so it should not affect any existing subclasses.
Of interest:
- Any properties which are designed to be overridden by subclasses are implemented using a local `@protoProp` decorator. That means they are applied to the prototype, so that they can be overridden in subclasses by both legacy `.extend()` prototype extensions, and by modern native-class fields.
- New class decorators are introduced: `@selectKitOptions` and `@pluginApiIdentifiers`. These are native class versions of the legacy `concatenatedProperties` system. This follows the pattern Ember has introduced for `@className`, `@classNameBindings`, etc.
This reverts commit 20780a1eee.
* SECURITY: re-adds accidentally reverted commit:
03d26cd6: ensure embed_url contains valid http(s) uri
* when the merge commit e62a85cf was reverted, git chose the 2660c2e2 parent to land on
instead of the 03d26cd6 parent (which contains security fixes)
