RFR: 8258777: SkinBase: add api to un-/register invalidation-/listChange listeners [v6]

[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)

Jeanette Winzenburg has updated the pull request incrementally with one additional commit since the last revision:

  changed javadoc of unregister (invalidation only)

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

Changes:
  - all: https://git.openjdk.java.net/jfx/pull/409/files
  - new: https://git.openjdk.java.net/jfx/pull/409/files/cf3a0228..e7849b21

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=409&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=409&range=04-05

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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