RFR: 7903300: Add test library support to jtreg plugin

[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

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Commit messages:
 - CODETOOLS-7903300

Changes: https://git.openjdk.org/jtreg/pull/117/files
 Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=117&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903300
  Stats: 124 lines in 3 files changed: 118 ins; 1 del; 5 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