[Ada] Fix the parsing for delta aggregate

[Ada] Fix the parsing for delta aggregate

In Ada 2022, delta aggregate must use parentheses not square brackets
except array delta aggregates.

gcc/ada/

	* gen_il-gen-gen_nodes.adb (Gen_IL.Gen.Gen_Nodes): Add
	Is_Homogeneous_Aggregate field for N_Delta_Aggregate nodes.
	* par-ch4.adb (P_Aggregate_Or_Paren_Expr): Minor reformatting.
	* sem_aggr.adb (Resolve_Delta_Aggregate): Reject square brackets
	for record aggregate.
	(Resolve_Record_Aggregate): Uniformise error message.