Make `init_scope` preserve the active name scope.

This ensures that operations nested under an `init_scope` do not ignore name scopes that were opened in a function-building graph. In light of cl/183320576, which causes `tfe.defun` to automatically hoist variables out of its function-building graph, this change also eliminates logic in make_template that special-cased the first call when `create_graph_function` was True.

PiperOrigin-RevId: 183680794