RFR: CODETOOLS-7903260: Fix support for JUnit tests in a system module

[Jonathan Gibbons]

Please review a simple patch to allow a directory of TestNG or JUnit tests to be patched into a system module, in order to access package-private API.

The patch is just to export the package containing the patched test to the possibly-unnamed module containing the library code to run the tests.

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Commit messages:
 - CODETOOLS-7903260: Fix support for JUnit tests in a system module

Changes: https://git.openjdk.org/jtreg/pull/105/files
 Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=105&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903260
  Stats: 7 lines in 1 file changed: 7 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jtreg/pull/105.diff
  Fetch: git fetch https://git.openjdk.org/jtreg pull/105/head:pull/105

PR: https://git.openjdk.org/jtreg/pull/105