RFR: 8296919: Make system tests that detect memory leaks more robust by using JMemoryBuddy utility [v2]

[Lukasz Kostyra]

> Verified these changes on all platforms and saw no abnormalities in test execution.
> 
> This change is based on a preliminary patch done by @aghaisas , with some minor changes and the addition of one Leak-related web test. EventListenerLeak test was not touched, as it is a separate manual test app instead of a JUnit test.

Lukasz Kostyra has updated the pull request incrementally with one additional commit since the last revision:

  Address review issues
  
  * JMemoryBuddy now has helpers for arrays of WeakReference, ArrayList
    of WeakReference and vararg WeakReferences
  * Updated copyright years in some files which were missed in previous
    changes

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1121/files
  - new: https://git.openjdk.org/jfx/pull/1121/files/fbee1d22..158ed40a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1121&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1121&range=00-01

  Stats: 39 lines in 7 files changed: 20 ins; 12 del; 7 mod
  Patch: https://git.openjdk.org/jfx/pull/1121.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1121/head:pull/1121

PR: https://git.openjdk.org/jfx/pull/1121