flesh out perlexperiment.pod

[p5pRT]

Migrated from rt.perl.org#116473 (status was 'new')

Searchable as RT116473$

[p5pRT]

From @rjbs

pod/perlexperiment.pod can be really useful if there was a bit more
evidence, paving the way for future deprecations and policy.

Go through perlexperiment (in the blead branch!) and, for each feature,
check whether the feature is announced as an experimental feature in the
perldelta for the version cited. If so, add that as a note. If not, find
out where it was announced as experimental and note that.

For features that were promoted to non-experimental or removed entirely,
make a note of that, too.