RFR: 8274274: Update JavaFX test framework to JUnit 5

[John Hendrikx]

I've added JUnit 5 as a test dependency and made sure that the JUnit 4 tests still work.  Also added a single JUnit 5 tests, and confirmed it works.

I've updated the Eclipse project file for the base module only.

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Commit messages:
 - Add JUnit 5

Changes: https://git.openjdk.java.net/jfx/pull/633/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=633&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274274
  Stats: 141 lines in 4 files changed: 141 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jfx/pull/633.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/633/head:pull/633

PR: https://git.openjdk.java.net/jfx/pull/633