[Ada] Bad handling of array sliding in aggregate

[Ada] Bad handling of array sliding in aggregate

gcc/ada/

	* exp_aggr.adb (Collect_Initialization_Statements): Removed.
	(Convert_Aggr_In_Object_Decl, Expand_Array_Aggregate): Fix
	creation and insertion of Initialization_Statements.  Do not set
	Initialization_Statements when a transient scope is involved.
	Move processing of Array_Slice here.  Ensure that an object with
	an Array_Slice call gets its array component initialized.  Add
	comments.
	* exp_ch7.adb: Update comments.
	(Store_Actions_In_Scope): Deal properly with an empty list which
	might now be generated by Convert_Aggr_In_Object_Decl.
	* exp_ch3.adb: Update comments.
	(Expand_N_Object_Declaration): Remove processing of Array_Slice.