RFR: JDK-8302355: Public API for Toolkit.canStartNestedEventLoop()

[Johan Vos]

On Mon, 13 Feb 2023 19:31:56 GMT, Marius Hanl <mhanl at openjdk.org> wrote:

> This PR adds the last missing method for dealing with nested event loops.
> As also written in the ticket, there is currently no (public) way to find out whether it is safe to start an event loop now or not.
> Classes like `Dialog` check via `Toolkit.getToolkit().canStartNestedEventLoop()` (sun api), if it safe to start a nested event loop before doing so.

I am in favor of this addition:
1. it adds functionality that is useful and otherwise hard to achieve in a generic way (I totally agree with the showing a Dialog in a TimeLine case). 
2. it is non-intrusive, as it is not allowing to change internal state (it simply queries the state).

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PR: https://git.openjdk.org/jfx/pull/1031