Support change~branch~id in query syntax

It is odd that we describe this in the REST API as a canonical way of
referring to a change, but don't support it in the query syntax. Since
the query parser is also used by the /r handler, this fixes that there
as well.

Unlike in the ChangesCollection parser, allow prefix searches for the
id portion, to be consistent with other search operators.

Change-Id: I55e1cc33caf907cb0ff17dae7a81a46156b6f562

gerrit-antlr/src/main/antlr3/com/google/gerrit/server/query/Query.g

@@ -188,6 +188,6 @@ fragment NON_WORD
      | '?'
      | '[' | ']'
      | '{' | '}'
-     | '~'
+     // | '~' permit
      )
   ;