Non-nil indicates that there has been (at least one) explicit
declaration of this name in this scope. In this case,
decl is the corresponding declaration; it might be a vl-portdecl, a vl-vardecl, a vl-fundecl, etc.
direct-pkg — maybe-string
When non-nil, this entry is directly import from the package
name direct-pkg, i.e., import foo::bar.
This entry is imported via import foo::* statements from
each of packages named in wildpkgs.
We used to eagerly compute this, but in the common case where
there are lots of imports of big packages and relatively few
uses of them, this isn't efficient. So vl-lexscope-find
computes this lazily instead.
