`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.
-------------
Commit messages:
- Optimize removeAll/retainAll for Observable{List/Set/Map}Wrapper
- Failing test
Changes: https://git.openjdk.java.net/jfx/pull/751/files
Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=751&range=00
Issue: https://bugs.openjdk.java.net/browse/JDK-8283063
Stats: 293 lines in 6 files changed: 290 ins; 0 del; 3 mod
Patch: https://git.openjdk.java.net/jfx/pull/751.diff
Fetch: git fetch https://git.openjdk.java.net/jfx pull/751/head:pull/751
PR: https://git.openjdk.java.net/jfx/pull/751
