Trac #9878: Make the static form illegal in interpreted mode.

Summary:
The entries of the static pointers table are expected to exist as
object code. Thus we have ghci complain with an intelligible error
message if the static form is used in interpreted mode.

It also includes a fix to keysHashTable in Hash.c which could cause a
crash. The iteration of the hashtable internals was incorrect. This
patch has the function keysHashTable imitate the iteration in
freeHashTable.

Finally, we submit here some minor edits to comments and
GHC.StaticPtr.StaticPtrInfo field names.

Authored-by: Alexander Vershilov <alexander.vershilov@tweag.>
Authored-by: Facundo Domínguez <facundo.dominguez@tweag.io>

Test Plan: ./validate

Reviewers: simonpj, hvr, austin

Reviewed By: austin

Subscribers: carter, thomie, qnikst, mboes

Differential Revision: https://phabricator.haskell.org/D586

GHC Trac Issues: #9878

(cherry picked from commit fffbf062)