Initial version of storing SourceElements in descriptors

Introduce SourceElement, JavaSourceElementFactory, DeclarationDescriptorWithSource
Implement getSource() for eager, lazy and java descriptors
Rewrite BindingContextUtils.descriptorToDeclaration utilities family to use SourceElement for getting PSI

Remove DESCRIPTOR_TO_DECLARATION context key
Refactor: Remove context parameter from BindingContextUtils.descriptorToDeclaration utilities family