This PR implements two new default methods on `ObservableList` to be able to 
replace elements at a given position or within a specified range.

Justification for this change is to allow an `ObservableList` to be bulk 
modified in a single `ListChangeListener` call back.  In this way the callbacks 
don't observe the list changing its size from S to S-X back to S again(*). 
Currently the only way to bulk replace a range of items is to remove X items 
then add X items, resulting not in two listener callbacks in between which the 
size of the list can be observed to change.

The other alternative is to call `set` individually for each item, which 
results in many change notifications.

With the addition of this PR, and the changes in 
`ModifiableObservableListBase`, replacing a range of items becomes a single 
change callback.

(*) The list may indeed change size still as plain `List` does not have 
`setAll` operations; size listeners may observe this, but it will no longer be 
observable from a `ListChangeListener` due to multiple separate callbacks.

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

Commit messages:
 - Implement setAll with range for ObservableList

Changes: https://git.openjdk.org/jfx/pull/1937/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1937&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8091429
  Stats: 134 lines in 3 files changed: 133 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1937.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1937/head:pull/1937

PR: https://git.openjdk.org/jfx/pull/1937

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