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.
------------- Commit messages: - JDK-8302355: Public API for Toolkit.canStartNestedEventLoop() Changes: https://git.openjdk.org/jfx/pull/1031/files Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1031&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8302355 Stats: 13 lines in 1 file changed: 12 ins; 0 del; 1 mod Patch: https://git.openjdk.org/jfx/pull/1031.diff Fetch: git fetch https://git.openjdk.org/jfx pull/1031/head:pull/1031 PR: https://git.openjdk.org/jfx/pull/1031
