needed to implement @PreDestroy

It is necessary to make NamespaceFactoryImpl independent from TopDownAnalysisContext

JavaDescriptorResolver now lives in the same context as TopDownAnalyzer

* extract NamespaceFactory from TypeHierarchyResolver
* implement NamespaceFactory.createNamespaceDescriptorPathIfNeeded(FqName)
* FqName .path() and .pathSegments() utilities

* required parameters have @NotNull annotation generated
* parameters are required by default

* ModuleDescrpiptor now lives in context
* ns parent is module descriptor iff ns is root ns
* minor test enhancements