Update inert_solved_dicts for ImplicitParams

When adding an implicit parameter dictionary to the inert set, we must
make sure that it replaces any previous implicit parameter dictionaries
that overlap, in order to get the appropriate shadowing behaviour, as in

  let ?x = 1 in let ?x = 2 in ?x

We were already doing this for inert_cans, but we weren't doing the same
thing for inert_solved_dicts, which lead to the bug reported in #23761.

The fix is thus to make sure that, when handling an implicit parameter
dictionary in updInertDicts, we update **both** inert_cans and
inert_solved_dicts to ensure a new implicit parameter dictionary
correctly shadows old ones.

Fixes #23761