[Ada] Update categorization of implementation restrictions

[Ada] Update categorization of implementation restrictions

Some of the restrictions were initially implemented as specific to GNAT,
but now they are part of Ada; likewise, some of recently added
restrictions were considered to be part of Ada, but are not yet in the
standard. This patch updates their categorization based on Ada 202x
Draft 32.

Only a No_Implementation_Restrictions restriction, which is specific to
GNAT, is affected.

Cleanup related to a new restriction No_Uninitialized_Local_Scalars.

gcc/ada/

	* libgnat/s-rident.ads (Implementation_Restriction): Remove
	No_Dynamic_Attachment, No_Implementation_Attributes,
	No_Implementation_Pragmas, No_Local_Protected_Objects,
	No_Protected_Type_Allocators, No_Relative_Delay,
	No_Requeue_Statements, No_Select_Statements,
	No_Task_Termination, Pure_Barriers and Simple_Barriers; add
	No_Dynamic_Sized_Objects,
	No_Implicit_Protected_Object_Allocations,
	No_Implicit_Task_Allocations, No_Task_At_Interrupt_Priority and
	Static_Dispatch_Tables; sort alphabetically.
	* restrict.ads (Restriction_Id): Change Pure_Barriers and
	No_Task_Termination from GNAT to Ada restrictions.