ICE Fix #16562

Fixes #16562

Detect ty_err in fixup_substs and return None instead of failing.
In search_for_vtable return vtable_error in both early and non-early
if fixup_substs returns None. This was asserting previously. I don't
know anything about the early vs. non-early stages and whether this
is significant or not.

Reduced the amount of data being printed to the debug log in
tydecode.rs. It was printing several megabytes of metadata.