[bindings] Figure out in-file structs and enums before processing

[bindings] Figure out in-file structs and enums before processing

Previously, types which were declared and used in the same file
would fail if the use was before the declaration. This makes sense
in a few cases where a "parent" class returns a reference to a
"child" class and there's no reason we shouldn't support it.

This change adds a second pass to our file processing which gathers
the structs and enums whicha re declared in the file and adds them
to the type resolver first, before doing the real conversion.