c++, coroutines: Make analyze_fn_params into a class method.

This continues code cleanups and migration to encapsulation of the
whole coroutine transform.

gcc/cp/ChangeLog:

	* coroutines.cc (analyze_fn_parms): Move from free function..
	(cp_coroutine_transform::analyze_fn_parms):... to method.
	(cp_coroutine_transform::apply_transforms): Adjust call to
	analyze_fn_parms.
	* coroutines.h: Declare analyze_fn_parms.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
(cherry picked from commit 2a8af97e3528f812201687334f64b27b94d01271)