[jfx11u] RFR: 8280275: JUnit5 tests using Assumptions API fail to compile in some cases

[Kevin Rushforth]

This PR is dependent on #97 so it is in Draft for now. Once #97 is integrated, I will rebase this and submit it, at which time it will be a clean backport, and the diffs will only show the updated test.

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Commit messages:
 - 8280275: JUnit5 tests using Assumptions API fail to compile in some cases

Changes: https://git.openjdk.java.net/jfx11u/pull/98/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx11u&pr=98&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280275
  Stats: 6 lines in 2 files changed: 4 ins; 1 del; 1 mod
  Patch: https://git.openjdk.java.net/jfx11u/pull/98.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx11u pull/98/head:pull/98

PR: https://git.openjdk.java.net/jfx11u/pull/98