Add create_and_copy_2d_grid_cross test; emulate cross for perl5

This is the third benchmark inspired by the slowness of rc-forest-fire,
in this case testing creation and copying of 2D grids using for/cross
to iterate over the grids.

Because Perl 5 has no real iterator-style cross operator, I also add a
cross-of-ranges emulation based on an iterating closure and use it for
the perl5 variant of this test and visit_2d_indices_cross.
Add forest-fire tag to rc-forest-fire related tests

This allows `./bench --tests-tagged=forest-fire time ...` to time all
tests related to rc-forest-fire (including the original) when working
on improving performance of constructions stressed by rc-forest-fire.

Also add a few missing tags to rc-forest-fire itself.
Add nqp variant of cross emulation

Extend the technique used for Perl 5 to work for NQP as well.  Also
increase the starting SCALE for visit_2d_indices_cross, as nqp and
perl5 were producing nonsense timings for such low SCALE values.