Fix sharing of 'IfaceTyConInfo' during core to iface type translation

During heap analysis, we noticed that during generation of
'mi_extra_decls' we have lots of duplicates for the instances:

* `IfaceTyConInfo NotPromoted IfaceNormalTyCon`
* `IfaceTyConInfo IsPromoted IfaceNormalTyCon`

which should be shared instead of duplicated. This duplication increased
the number of live bytes by around 200MB while loading the agda codebase
into GHCi.

These instances are created during `CoreToIface` translation, in
particular `toIfaceTyCon`.

The generated core looks like:

    toIfaceTyCon
      = \ tc_sjJw ->
          case $wtoIfaceTyCon tc_sjJw of
          { (# ww_sjJz, ww1_sjNL, ww2_sjNM #) ->
          IfaceTyCon ww_sjJz (IfaceTyConInfo ww1_sjNL ww2_sjNM)
          }

whichs removes causes the sharing to work propery.

Adding explicit sharing, with NOINLINE annotations, changes the core to:

    toIfaceTyCon
      = \ tc_sjJq ->
          case $wtoIfaceTyCon tc_sjJq of { (# ww_sjNB, ww1_sjNC #) ->
          IfaceTyCon ww_sjNB ww1_sjNC
          }

which looks much more like sharing is happening.
We confirmed via ghc-debug that all duplications were eliminated and the
number of live bytes are noticeably reduced.