Add the sparseRange() utility function

This helper allows to use for-loops with structured bindings for sparse ranges R whose iterators it provide an it->index() method, like this

for(auto&& [A_i, i] : sparseRange(R))
  doSomethingWithValueAndIndex(A_i, i);

This also adds a test and fixes the placement of the range-utilities in the appropriate doxygen group to make them easier to discover.

added feature label

This implements sparseRange as proposed in !781 (merged).

mentioned in merge request !781 (merged)

assigned to @oliver.sander

@oliver Since you had problems with your manual implementation of sparseRange, please check if this one works for you.

@carsten.graeser , this one works. The test is at https://gitlab.mn.tu-dresden.de/paraphase/dune-fracture-phasefields/-/merge_requests/20 .

Any objections to merging this?

No, please go ahead.

merged

mentioned in commit 90cbf00f