Add @api stable annotations for the ol.control namespace

[elemoine]

This PR adds @api stable annotations to constructors and methods of the ol.control package.

Please review.

[tschaub]

Ok, given that we agree that the @api stable annotation on something like olx.control.DefaultsOptions doesn't currently mean that all of the options are stable, I think this is good to merge. #2578 deals with stability markers on olx object properties.

[elemoine]

Ok, given that we agree that the @api stable annotation on something like olx.control.DefaultsOptions doesn't currently mean that all of the options are stable, I think this is good to merge. #2578 deals with stability markers on olx object properties.

Agree.