Add comprehensive 'report-prereqs'-like tooling

Add comprehensive 'report-prereqs'-like tooling

Unlike what is currently available in various Dzil plugins, this is more of
a descendent of Test::DiagINC - it tries to load as much as possible and
subsequently reports on whatever can be found in the symtable.

There is no (and never will be any) attempt made to validate if all modules
listed in the various METAs are in fact available (this is what the rest of
the test suite is for).

Module versions are broken up into groups depending on their place in @INC,
without leaking the contents of @INC itself.