RFR: 8283063: Optimize Observable{List/Set/Map}Wrapper.retainAll/removeAll [v2]

[Michael Strauß]

> `Observable{List/Set/Map}Wrapper.retainAll/removeAll` can be optimized for some edge cases.
> 
> 1. `removeAll(c)`:
> This is a no-op if 'c' is empty.
> For `ObservableListWrapper`, returning early skips an object allocation. For `ObservableSetWrapper` and `ObservableMapWrapper`, returning early prevents an enumeration of the entire collection.
> 
> 2. `retainAll(c)`:
> This is a no-op if the backing collection is empty, or equivalent to `clear()` if `c` is empty.
> 
> I've added some tests to verify the optimized behavior for each of the three classes.

Michael Strauß has updated the pull request incrementally with two additional commits since the last revision:

 - address review comments
 - refactored removeAll/retainAll optimizations

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/751/files
  - new: https://git.openjdk.org/jfx/pull/751/files/af84b648..9a0e29a4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=751&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=751&range=00-01

  Stats: 679 lines in 11 files changed: 573 ins; 72 del; 34 mod
  Patch: https://git.openjdk.org/jfx/pull/751.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/751/head:pull/751

PR: https://git.openjdk.org/jfx/pull/751