[hist] Implement RBinIndexRange

[hahnjo]

The interface allows convenient iteration over RBinIndex.

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A bit of context on constructing RBinIndexRange: Initially I considered a plain constructor and / or static factory methods that would allow creating bin index ranges without an axis object. That was kind of awkward because of conventions (end is exclusive, so to have a range including RBinIndex::Overflow() we use the invalid RBinIndex), the difference in axis configurations (are flow bins enabled?), and in axis types (a categorical axis will only have an overflow, but not an underflow bin). When discussing with @hageboeck, we came to the conclusion that (for the moment) we prefer creating RBinIndexRanges from axis objects. This can also enforce a number of constraints, for example that the normal bins are actually valid for the given axis configuration. To simplify testing, I opted for a Internal::CreateBinIndexRange that is also used by Get{Normal,Full}Range.

[github-actions]

Test Results

    21 files      21 suites   3d 15h 6m 48s ⏱️
 3 561 tests  3 424 ✅  0 💤 137 ❌
73 028 runs  72 874 ✅ 17 💤 137 ❌

For more details on these failures, see this check.

Results for commit 8368d62.

♻️ This comment has been updated with latest results.

[hageboeck]

Almost nothing to add. 👍