vect: Refactor to allow internal_fn's

Refactor vect-patterns to allow patterns to be internal_fns starting
with widening_plus/minus patterns

2023-06-05  Andre Vieira  <andre.simoesdiasvieira@arm.com>
	    Joel Hutton  <joel.hutton@arm.com>

gcc/ChangeLog:
	* tree-vect-patterns.cc: Add include for gimple-iterator.
	(vect_recog_widen_op_pattern): Refactor to use code_helper.
	(vect_gimple_build): New function.
	* tree-vect-stmts.cc (simple_integer_narrowing): Refactor to use
	code_helper.
	(vectorizable_call): Likewise.
	(vect_gen_widened_results_half): Likewise.
	(vect_create_vectorized_demotion_stmts): Likewise.
	(vect_create_vectorized_promotion_stmts): Likewise.
	(vect_create_half_widening_stmts): Likewise.
	(vectorizable_conversion): Likewise.
	(supportable_widening_operation): Likewise.
	(supportable_narrowing_operation): Likewise.
	* tree-vectorizer.h (supportable_widening_operation): Change
	prototype to use code_helper.
	(supportable_narrowing_operation): Likewise.
	(vect_gimple_build): New function prototype.
	* tree.h (code_helper::safe_as_tree_code): New function.
	(code_helper::safe_as_fn_code): New function.