implement the `ResolventOps` methods for chalk integration

[nikomatsakis]

The methods in the ResolventOps trait are currently unimplemented:

rust/src/librustc_traits/chalk_context.rs

Lines 275 to 297 in e1643a8

	impl context::ResolventOps<ChalkArenas<'gcx>, ChalkArenas<'tcx>>
	for ChalkInferenceContext<'cx, 'gcx, 'tcx>
	{
	fn resolvent_clause(
	&mut self,
	_environment: &ty::ParamEnv<'tcx>,
	_goal: &DomainGoal<'tcx>,
	_subst: &CanonicalVarValues<'tcx>,
	_clause: &ProgramClause<'tcx>,
	) -> chalk_engine::fallible::Fallible<Canonical<'gcx, ChalkExClause<'gcx>>> {
	panic!()
	}
	fn apply_answer_subst(
	&mut self,
	_ex_clause: ChalkExClause<'tcx>,
	_selected_goal: &ty::ParamEnvAnd<'tcx, Goal<'tcx>>,
	_answer_table_goal: &Canonical<'gcx, ty::ParamEnvAnd<'gcx, Goal<'gcx>>>,
	_canonical_answer_subst: &Canonical<'gcx, ConstrainedSubst<'gcx>>,
	) -> chalk_engine::fallible::Fallible<ChalkExClause<'tcx>> {
	panic!()
	}
	}

These methods perform various unification-like operations and will need to be implemented in rustc.

[nikomatsakis]

Another similar case is that the unify_parameters method must be implemented:

rust/src/librustc_traits/chalk_context.rs

Lines 428 to 435 in e1643a8

	fn unify_parameters(
	&mut self,
	_environment: &ty::ParamEnv<'tcx>,
	_a: &Kind<'tcx>,
	_b: &Kind<'tcx>,
	) -> ChalkEngineFallible<InferOk<'tcx, ()>> {
	panic!()
	}