[4.2] Obsolete unsafeArithmetic operations on Integers. (#19425)

* Obsolete unsafeArithmetic oeprations on Integers.

* 4.2.1 -> 4.2

Author: stephentyrone

stdlib/public/core/Integers.swift.gyb

@@ -2938,6 +2938,7 @@ ${assignmentOperatorComment(x.operator, True)}
 #endif
 // end of FIXME(integers)
 
+@available(swift, deprecated: 4.2, obsoleted: 5)
 ${unsafeOperationComment(x.operator)}
   @inlinable // FIXME(sil-serialize-all)
   @_transparent