[accordion]: add disabled property to CDK accordion-item

[henetiriki]

Proposal:

Move common-behaviors to CDK.

What is the use-case or motivation for changing an existing behavior?

Accordion (and possibly other CDK components) need access to the disabled property on directives - see #7461

[henetiriki]

@jelbourn / @josephperrott - which of the other common behaviors do you see being useful in the CDK?

Acceptable for the Constructor type to move along and be made public, or is duplication here okay?

[josephperrott]

@ouq77 At this point I think we should just move the disabled properties (CanDisable, mixinDisabled) at this point. We can move the others as its determined they are needed and make sense to move.

You should be fine to also move the Constructor typing over as well.

[jelbourn]

For the time being I'd rather re-create those properties than move the mixins to the cdk until we have a greater catalog of common behaviors.