analyzer: add logging to get_representative_path_var

This was very helpful when debugging the cast_region::m_original_region
removal, but is probably too verbose to enable except by hand on
specific calls to get_representative_tree.

gcc/analyzer/ChangeLog:
	* engine.cc (impl_region_model_context::on_state_leak): Pass nullptr
	to get_representative_path_var.
	* region-model.cc (region_model::get_representative_path_var_1):
	Add logger param and use it in both overloads.
	(region_model::get_representative_path_var): Likewise.
	(region_model::get_representative_tree): Likewise.
	(selftest::test_get_representative_path_var): Pass nullptr to
	get_representative_path_var.
	* region-model.h (region_model::get_representative_tree): Add
	optional logger param to both overloads.
	(region_model::get_representative_path_var): Add logger param to
	both overloads.
	(region_model::get_representative_path_var_1): Likewise.
	* store.cc (binding_cluster::get_representative_path_vars): Add
	logger param and use it.
	(store::get_representative_path_vars): Likewise.
	* store.h (binding_cluster::get_representative_path_vars): Add
	logger param.
	(store::get_representative_path_vars): Likewise.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>