RFR: 7903300: Add test library support to jtreg plugin [v2]

[Guoxiong Li]

> Hi all,
> 
> Currently, when we open a jtreg test file which uses the JUnit or TestNG, the plugin can't identify the related classes of the JUnit or TestNG. So the statement such as `import org.junit.Test` is marked as red with error message `Cannot resolve symbol 'junit'`.
> 
> This patch adds the jtreg libraries directory to the lib path of the `Jetbrains IDEA` when opening the JUnit or TestNG test files so that the `Jetbrains IDEA` can identify the related classes.
> 
> Thanks for taking the time to review.
> 
> Best Regards,
> -- Guoxiong

Guoxiong Li has updated the pull request incrementally with two additional commits since the last revision:

 - Bump the version and revise notes.
 - Adjust the api name. Fix the possible NPE and remove duplicated entries.

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Changes:
  - all: https://git.openjdk.org/jtreg/pull/117/files
  - new: https://git.openjdk.org/jtreg/pull/117/files/7703b0e9..e0d865af

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jtreg&pr=117&range=01
 - incr: https://webrevs.openjdk.org/?repo=jtreg&pr=117&range=00-01

  Stats: 29 lines in 4 files changed: 18 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/jtreg/pull/117.diff
  Fetch: git fetch https://git.openjdk.org/jtreg pull/117/head:pull/117

PR: https://git.openjdk.org/jtreg/pull/117