[Ada] Handle implicit moves in SPARK ownership pointer support

Allocator expressions and sub-expressions of (extension) aggregates are
implicitly the source of assignments in Ada. Thus, they should be moved
when of a deep type when checking ownership rules in SPARK.

There is no impact on compilation.

2019-07-09  Yannick Moy  <moy@adacore.com>

gcc/ada/

	* sem_spark.adb (Check_Expression): Handle correctly implicit
	assignments as part of allocators and (extension) aggregates.
	(Get_Root_Object): Adapt for new path expressions.
	(Is_Path_Expression): Return True for (extension) aggregate.

From-SVN: r273271

gcc/ada/ChangeLog

+2019-07-09  Yannick Moy  <moy@adacore.com>
+
+	* sem_spark.adb (Check_Expression): Handle correctly implicit
+	assignments as part of allocators and (extension) aggregates.
+	(Get_Root_Object): Adapt for new path expressions.
+	(Is_Path_Expression): Return True for (extension) aggregate.
+
 2019-07-09  Piotr Trojanek  <trojanek@adacore.com>
 
 	* einfo.ads: Fix a typo.