Deprecate DoFTools::extract_boundary_dofs() with std::vector<bool> argument

[bangerth]

We have slowly been replacing these by functions using IndexSet instead, and indeed such a function already exists. The function here is not particularly widely used.

/rebuild

[masterleinad]

Looks good to me.

[masterleinad]

/home/runner/work/dealii/dealii/examples/step-11/step-11.cc:150:36: error: ‘void dealii::DoFTools::extract_boundary_dofs(const dealii::DoFHandler<dim, spacedim>&, const dealii::ComponentMask&, std::vector<bool>&, const std::set<unsigned int>&) [with int dim = 2; int spacedim = 2]’ is deprecated [-Werror=deprecated-declarations]
     DoFTools::extract_boundary_dofs(dof_handler,
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~
                                     ComponentMask(),
                                     ~~~~~~~~~~~~~~~~
                                     boundary_dofs);
                                     ~~~~~~~~~~~~~~
In file included from /home/runner/work/dealii/dealii/examples/step-11/step-11.cc:35:0:
/home/runner/work/dealii/dealii/include/deal.II/dofs/dof_tools.h:1459:3: note: declared here
   extract_boundary_dofs(const DoFHandler<dim, spacedim> &   dof_handler,
   ^~~~~~~~~~~~~~~~~~~~~
cc1plus: all warnings being treated as errors

[bangerth]

Oh, I fix this place in #11996. Maybe I should just combine these two patches -- so done. Merging this patch is then also going to close #11996. That would also mean that if someone approved #11996, and since we already have two approvals for this PR here in its previous state, that the now combined patch here should be acceptable.

[jppelteret]

I've removed the "Reviewed and ready to merge" label because I guess that you want to squash some of these commits, @bangerth?

[bangerth]

I reduced the number of commits a bit, but what I have now is pretty self-contained in each commit.

[masterleinad]

Looks good to me.