RFR: 8285503: SwingNodeDnDMemoryLeakTest::testSwingNodeMemoryLeak fails sometimes [v2]

[Ajit Ghaisas]

> Root cause: The test unreliability comes from the 250ms sleep between `System.gc()` calls.
> Other system tests such as `TabPaneHeaderLeakTest`, `AccordionTitlePaneLeakTest` and `ShapeViewOrderLeakTest` etc sleep for 500ms between `System.gc()` calls.
> 
> Fix:
> - Increased the sleep time to 500ms between `System.gc()` calls.
> - Reduced the number of SwingNodes by half as an additional step towards making the test lighter.
> 
> Testing: This test used to fail on my macBook all the time if ran as part of a full system test run. I executed full test runs 5 times with above changes and no failure was observed.

Ajit Ghaisas has updated the pull request incrementally with one additional commit since the last revision:

  Revert total swingnode count to 10 in test

-------------

Changes:
  - all: https://git.openjdk.org/jfx/pull/946/files
  - new: https://git.openjdk.org/jfx/pull/946/files/14309ed7..0b98be18

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=946&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=946&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/946.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/946/head:pull/946

PR: https://git.openjdk.org/jfx/pull/946