Disallow importing from types when reexport is involved
auto merge of #15733 : sanxiyn/rust/use-from-type, r=alexcrichton

Importing from types was disallowed in #6462. Flag was set for paths whether it is a module or a type. Type flag was set when impl was seen. The problem is, for cross-crate situations, when reexport is involved, it is possible that impl is seen too late because metadata is loaded lazily.

Fix #15664.