RFR: 8248381: Create a daemon thread for MonocleTimer

[Kevin Rushforth]

On Fri, 26 Jun 2020 03:50:02 GMT, John Neffenger <github.com+1413266+jgneff at openjdk.org> wrote:

> Fixes [JDK-8248381](https://bugs.openjdk.java.net/browse/JDK-8248381).

It looks simple enough for a single reviewer. Since it is in Monocle, @johanvos will probably want to review it.

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PR: https://git.openjdk.java.net/jfx/pull/256