RFR: 8290310: ChangeListener events are incorrect or misleading when a nested change occurs

[Michael Strauß]

On Sun, 17 Jul 2022 20:59:46 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

> This contains the following:
> - Nested changes or invalidations using ExpressionHelper are delayed until the current emission completes
>   - This fixes odd change events being produced (with incorrect oldValue)
>   - Also fixes a bug in ExpressionHelper where a nested change would unlock the listener list early, which could cause a `ConcurrentModificationException` if a nested change was combined with a remove/add listener call
> - A test for ExpressionHelper to verify the new behavior
> - A test for all *Property and *Binding classes that verifies correct listener behavior at the API level (this tests gets 85% coverage on ExpressionHelper on its own, the only thing it is not testing is the locking behavior, which is not relevant at the API level).
> - A fix for `WebColorFieldSkin` which triggered a nested change which used a flag to prevent an event loop (I've changed it now to match how `DoubleFieldSkin` and `IntegerFieldSkin` do it

I've re-read the discussion on the [mailing list](https://mail.openjdk.org/pipermail/openjfx-dev/2022-July/034705.html). The approach as implemented in this PR is a good solution, as it has a very low implementation and runtime overhead, and gets us to having consistent histories for change listeners.

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Marked as reviewed by mstrauss (Committer).

PR: https://git.openjdk.org/jfx/pull/837