RFR: 8258777: SkinBase: add api to un-/register invalidation-/listChange listeners

[Jeanette Winzenburg]

Changes in Lambda..Handler:
- added api and implemenation to support invalidation and listChange listeners in the same way as changeListeners
- added java doc 
- added tests

Changes in SkinBase
- added api (and implementation delegating to the handler)
- copied java doc from the change listener un/register methods 
- added tests to verify that the new (and old) api is indeed delegating to the handler

Note that the null handling is slightly extended: all methods now can handle both null consumers (as before) and null observables (new) - this allows simplified code on rewiring "path" properties (see reference example in the issue)

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Commit messages:
 - 8258777: SkinBase: add api to un-/register invalidation-/listChange

Changes: https://git.openjdk.java.net/jfx/pull/409/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=409&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258777
  Stats: 970 lines in 6 files changed: 946 ins; 9 del; 15 mod
  Patch: https://git.openjdk.java.net/jfx/pull/409.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/409/head:pull/409

PR: https://git.openjdk.java.net/jfx/pull/409