ada: Transfer fix for pretty-printed parentheses from GNATprove to GNAT

ada: Transfer fix for pretty-printed parentheses from GNATprove to GNAT

Expressions with parentheses are notoriously problematic to
pretty-print. In GNATprove we had a post-processing fix for them,
but it is better to have this fix in the GNAT frontend repository
and apply it for CodePeer as well.

gcc/ada/

	* pprint.adb (Expression_Image): Move Count_Parentheses and
	Fix_Parentheses routines from GNATprove and apply them before
	returning the slice of a source code buffer.