StubToolkit breaks test

[John Hendrikx]

I found an old disabled test that is testing PrismTextLayout for which I 
have a PR outstanding (https://github.com/openjdk/jfx/pull/1236).

The test I think is useful, but is loading real fonts (Monaco and 
Tahoma).  Locally this works when I don't use the StubToolkit to run the 
test, and (I presume) may also work on the various build environments if 
those fonts are part of those environments (otherwise the test can be 
disabled with a JUnit 5 Assumption for platforms that lack these fonts 
-- the test would be useful even if it ran only in one environment as 
aside from the required fonts it is not OS specific).

However, in the build system, the test is run with the StubToolkit, 
which can't load real fonts (which I do really need for a proper test).  
The test therefore fails.

Is there a way to mark tests to not use the StubToolkit?

--John