libcst.metadata.Scope.get_qualified_names_for doesn't handle relative imports

[lpetre]

This also applies to QualifiedNameProvider. As far as I can tell, these types don't have the necessary context (ie full module name) to resolve relative imports.

libcst.helpers.get_absolute_module_for_import could resolve the proper name if we had access to a full module name for the scope.

Working:

>>> wrapper = cst.MetadataWrapper(cst.parse_module("from lib import a\na()"))
>>> scopes = wrapper.resolve(cst.metadata.ScopeProvider)
>>> scope_of_module = scopes[wrapper.module]
>>> a_call = wrapper.module.body[1].body[0].value
>>> scope_of_module.get_qualified_names_for(a_call)
{QualifiedName(name='lib.a', source=<QualifiedNameSource.IMPORT: 1>)}

Broken:

>>> wrapper = cst.MetadataWrapper(cst.parse_module("from . import a\na()"))
>>> scopes = wrapper.resolve(cst.metadata.ScopeProvider)
>>> scope_of_module = scopes[wrapper.module]
>>> a_call = wrapper.module.body[1].body[0].value
>>> scope_of_module.get_qualified_names_for(a_call)
{QualifiedName(name='a', source=<QualifiedNameSource.IMPORT: 1>)}

I believe this TODO is necessary to implement (somehow): https://github.com/Instagram/LibCST/blob/master/libcst/metadata/scope_provider.py#L298