python bindings for dirichlet values class

[rath3t]

Currently we have several useless method names in

ikarus/ikarus/python/dirichletvalues/dirichletvalues.hh

Lines 70 to 106 in fa0c806

	cls.def("fixBoundaryDOFs",
	[](DirichletValues& self, const std::function<void(Eigen::Ref<Eigen::VectorX<bool>>, int)>& f) {
	auto lambda = [&](BackendType& vec, const MultiIndex& indexGlobal) {
	// we explicitly only allow flat indices
	f(vec.vector(), indexGlobal[0]);
	};
	self.fixBoundaryDOFs(lambda);
	});
	cls.def("fixBoundaryDOFsUsingLocalView",
	[](DirichletValues& self,
	const std::function<void(Eigen::Ref<Eigen::VectorX<bool>>, int, LocalViewWrapper&)>& f) {
	auto lambda = [&](BackendType& vec, int localIndex, LocalView& lv) {
	auto lvWrapper = LocalViewWrapper(lv.globalBasis());
	// this can be simplified when
	// https://gitlab.dune-project.org/staging/dune-functions/-/merge_requests/418 becomes available
	pybind11::object obj = pybind11::cast(lv.element());
	lvWrapper.bind(obj);
	f(vec.vector(), localIndex, lvWrapper);
	};
	self.fixBoundaryDOFs(lambda);
	});
	cls.def(
	"fixBoundaryDOFsUsingLocalViewAndIntersection",
	[](DirichletValues& self,
	const std::function<void(Eigen::Ref<Eigen::VectorX<bool>>, int, LocalViewWrapper&, const Intersection&)>& f) {
	auto lambda = [&](BackendType& vec, int localIndex, LocalView& lv, const Intersection& intersection) {
	auto lvWrapper = LocalViewWrapper(lv.globalBasis());
	// this can be simplified when
	// https://gitlab.dune-project.org/staging/dune-functions/-/merge_requests/418 becomes available
	pybind11::object obj = pybind11::cast(lv.element());
	lvWrapper.bind(obj);
	f(vec.vector(), localIndex, lvWrapper, intersection);
	};
	self.fixBoundaryDOFs(lambda);
	});

These should be combined to fixBoundaryDOFs.
and also the simplifications from https://gitlab.dune-project.org/staging/dune-functions/-/merge_requests/418 are available and should be added.

Just rename all function to fixBoundaryDOFs and keep the lambdas might already work.

Otherwise accepting py::kwargs might also work. @henrij22 can you have a look?