[Ada] Ada2020: AI12-0304 Put_Image attrs of lang-def types

[Ada] Ada2020: AI12-0304 Put_Image attrs of lang-def types

gcc/ada/

	* libgnat/s-rannum.ads, libgnat/s-rannum.adb: Add Put_Image.
	This will be inherited by the language-defined packages
	Ada.Numerics.Discrete_Random and Ada.Numerics.Float_Random.
	* libgnat/a-convec.ads, libgnat/a-convec.adb: Add Put_Image.
	* libgnat/s-putima.ads: Add pragma Preelaborate, so this can be
	imported into containers packages.
	* libgnat/s-putima.adb: Move Digit to private part; otherwise
	reference to Base is illegal in Preelaborate generic.
	* exp_put_image.adb (Build_Record_Put_Image_Procedure): Use the
	base type.