RFR: 8285081: Improve XPath operators count accuracy

[Joe Wang]

Adjust how XPath operators are counted to improve accuracy. This change does not affect how XPath works. 

Test:  
     Tier2 passed;
     JCK XML tests passed.

-------------

Commit messages:
 - 8285081: Improve XPath operators count accuracy

Changes: https://git.openjdk.java.net/jdk/pull/9022/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=9022&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8285081
  Stats: 66 lines in 3 files changed: 43 ins; 3 del; 20 mod
  Patch: https://git.openjdk.java.net/jdk/pull/9022.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/9022/head:pull/9022

PR: https://git.openjdk.java.net/jdk/pull/9022