LPS-46683 Making liferay-staging tag library "private"

Hey Ray,

We had a discussion on zulip a while ago regarding if we need a liferay-staging tag library.

We do have an option in the portal to exclude a taglib from being copied to the portlets when we they are getting deployed, so that's the minimum I can do for this. The tag java files will still be public but to re-organize that it would be a way bigger refactoring.
I'm not sure if the ProviderType annotation can be applied to tag classes to indicate that they are not subject for extending or using outside, I haven't found any occurence of that between the tags.

With this change I'm sending to you at least the tag defintion will be exclusive to the portal, since we are using it internally.

Thanks,

Máté