Improve profile handling in switch lowering.

	PR tree-optimization/101301
	PR tree-optimization/103680

gcc/ChangeLog:

	* tree-switch-conversion.cc (bit_test_cluster::emit):
	Handle correctly remaining probability.
	(switch_decision_tree::try_switch_expansion): Fix BB's count
	where a cluster expansion happens.
	(switch_decision_tree::emit_cmp_and_jump_insns): Fill up also
	BB count.
	(switch_decision_tree::do_jump_if_equal): Likewise.
	(switch_decision_tree::emit_case_nodes): Handle special case
	for BT expansion which can also fallback to a default BB.
	* tree-switch-conversion.h (cluster::cluster): Add
	m_default_prob probability.