RFR: 8244195: [TEST_BUG] Convert the system tests TabPanePermuteGetTabsTest to unit test

[Ambarish Rapte]

As discussed [here](https://github.com/openjdk/jfx/pull/201#issuecomment-621772586) during #201 , This PR converts the
system tests in TabPanePermuteGetTabsTest.java to unit test.

Thanks @kleopatra , for providing the test. I have added few more tests and found few failures.
[JDK-8245528](https://bugs.openjdk.java.net/browse/JDK-8245528) is created to fix these failures, the failing tests are
currently ignored using this bug.

Please take a look.

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Commit messages:
 - 8244195: [TEST_BUG] Convert the system tests TabPanePermuteGetTabsTest to unit test

Changes: https://git.openjdk.java.net/jfx/pull/230/files
 Webrev: https://webrevs.openjdk.java.net/jfx/230/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8244195
  Stats: 660 lines in 4 files changed: 307 ins; 352 del; 1 mod
  Patch: https://git.openjdk.java.net/jfx/pull/230.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/230/head:pull/230

PR: https://git.openjdk.java.net/jfx/pull/230