feat(cdk-experimental/accordion): add accordion directives, example, and tests

[ok7sai]

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[github-actions]

Deployed dev-app for 1f2ebfc to: https://ng-dev-previews-comp--pr-angular-components-31134-dev-pemcmxw4.web.app

Note: As new commits are pushed to this pull request, this link is updated after the preview is rebuilt.

[mmalerba]

In the demo I see that if I:

• turn multi off
• select just item 2 in the select
• click item 1

It toggles item 2 closed even though item 2's trigger is disabled. Is that the correct behavior? (genuinely not sure). I think it feels odd to me because the intent of the disabled trigger is like "hey user, you can't change this", but then if they toggle a different item they actually can

[ok7sai]

In the demo I see that if I:

• turn multi off
• select just item 2 in the select
• click item 1

It toggles item 2 closed even though item 2's trigger is disabled. Is that the correct behavior? (genuinely not sure). I think it feels odd to me because the intent of the disabled trigger is like "hey user, you can't change this", but then if they toggle a different item they actually can

You are absolutely correct. Agree that the expansion state for a disabled trigger shouldn't be changed. Fixed in the Expansion behavior to ensure the disabled triggers are excluded from the state changes.