Improve type resolution performance

Method IType.resolveType(String typeName) is rather slow - it takes about 5ms for a class with ~20 imports and ~3 super types. For a middle size project with ~500 classes and ~100 type references per class it will take about 4 minutes to resolve all of them. We should try to do our best to resolve type in a simplified way and invoke IType.resolveType only when it fails.