Hiera functions: hiera_hash, hiera_array, hiera_include, hiera; with links to docs site for
additional information, more complete examples
(Maint) Make sure we don't execute pkglist in specs

During an uninstall, the aix and nim package providers execute pkglist,
which wasn't being stubbed out. This seems to only fail on windows but not
other platforms. Updated the tests accordingly.
Merge pull request #1523 from pdxmph/hiera_functions

(#15352) Documentation strings for hiera_hash, hiera_array, hiera_include, hiera