Ada: Fix missing implicit dereference for access-to-protected used as prefix

... of access-related attribute.  This is a regression present on all active
branches caused by a local resolution of the N_Selected_Component node.

gcc/ada/
	PR ada/124226
	* sem_res.adb (Resolve_Implicit_Dereference): Move declaration to...
	* sem_res.ads (Resolve_Implicit_Dereference): ...here.
	* sem_attr.adb (Resolve_Attribute) <Attribute_Access>: Also call
	Resolve_Implicit_Dereference when resolving a protected operation.

gcc/testsuite/
	* gnat.dg/protected_deref1.adb: New test.