Add YangConstants.operation{Input,Output}QName()

Add YangConstants.operation{Input,Output}QName()

Since we have QName.withModule(), we can optimize instantiation of
action/RPC input output statements by pre-validating the local name.

This is significantly faster than parsing the string via
StmtContextUtils.qnameFromArgument() and is useful for downstreams
which interaction with actions/RPCs.

Change-Id: If6da796df375f9785e05cb3cf901d64cccf2cfe5
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>
(cherry picked from commit 410be68c91e90c8a95f974d46303c45745e0784c)