Add multiple application support

Jersey supports just a single Application class, but Jakarta REST spec does not deny having multiple Application classes.

The change requires a refactoring of Jersey internals and it is rather a huge change. It might be handled by a proper InjectionManager, too. This does not look like a preferred solution, though.

Start by reviewing Jersey's internal handling of the Application class and the possible role of InjectionManager, as named in the issue. The work is complete when Jersey supports multiple Application classes in a way consistent with the Jakarta REST specification, with the required internal refactoring addressed.

Written by the indexing model from the issue text.