RFR: 7903744: Update various versions used by jtreg's IDEA plugin

[Chen Liang]

Now that ant is no longer bundled with IDEA, it has to be defined in a different way. And intellij IDEA changed their gradle plugin for IDE plugins so I did a migration to their new gradle plugin, which requires bumping Gradle.

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Commit messages:
 - Fix a few issues
 - 7903744: Update various versions used by jtreg's IDEA plugin

Changes: https://git.openjdk.org/jtreg/pull/201/files
  Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=201&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903744
  Stats: 56 lines in 7 files changed: 26 ins; 1 del; 29 mod
  Patch: https://git.openjdk.org/jtreg/pull/201.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/201/head:pull/201

PR: https://git.openjdk.org/jtreg/pull/201