ada: Improve ghost region creation for pragmas

ada: Improve ghost region creation for pragmas

gcc/ada/ChangeLog:

	* atree.adb (Mark_New_Ghost_Node): Set Is_Implicit_Ghost for
	all newly created nodes.
	* gen_il-fields.ads (Is_Implicit_Ghost): New attribute.
	* gen_il-gen-gen_entities.adb (Entity_Kind): Add Is_Implicit_Ghost
	attribute.
	* ghost.adb (Ghost_Policy_In_Effect): Implicit_Ghost_Entities inside
	pragmas get the ghost mode from the region isntead of the global
	ghost policy.
	(Ghost_Assertion_Level_In_Effect): New function that returns the
	applicable assertion level for the given entity in a similar manner
	as Ghost_Policy_In_Effect.
	(Install_Ghost_Region): Set Is_Inside_Statement_Or_Pragma attribute.
	(Mark_And_Set_Ghost_Body): Update the logic for deriving the ghost
	region.
	(Set_Ghost_Mode): Ignored pragmas attached to checked ghost entities
	now create an ignored ghost region. Pragmas attached to non-ghost
	entities create the ghost region based on the policy applied to the
	given pragma.
	* opt.ads (Ghost_Config_Type): add new attribute
	Is_Inside_Statement_Or_Pragama to track whether we should take the
	active ghost mode from the ghost region for implicit ghost entities.
	* sem_prag.adb (Analyze_Pragma): Mark entities that have an explicit
	ghost pragma as non-implicit ghost.