Given the test case
import { SomeType } from "somewhere.60";
import { Blah } from "foo.60";
and foo.60 trying to use "SomeType":
export Blah := SomeType {}
then the lookup for "SomeType" in foo.60 should fail. Instead it leaked
through the populated type registry when processing the dependencies for
the outer file.
This is fixed by ensuring that the type registry for a file only has the
global type registry as parent. To ensure that the test reliably covers
this, the import dependencies are now processed in declaration order
(hence the switch to IndexMap that preserves insertion order).
