RFR: JDK-8289948: Improve test coverage for XPath functions: Node Set Functions

[Bill Huang]

Provided coverage for XPath node set functions. Functions include:
- id()
- last()
- position()
- count()
- local-name()
- namespace-uri()
- name()

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

Commit messages:
 - Removed unwanted whitespaces.
 - Updated copyright header.
 - Created XPathExpFnTest.java for XPath functions and implemented test cases for node set functions.

Changes: https://git.openjdk.org/jdk/pull/9633/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9633&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8289948
  Stats: 215 lines in 2 files changed: 189 ins; 10 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/9633.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9633/head:pull/9633

PR: https://git.openjdk.org/jdk/pull/9633