Openjfx: all projects to use JUnit5 (Eclipse)

just noticed that the controls .classpath is missing an entry for JUnit5 - which are needed f.i. for PR 711 which added new tests using it.

The missing entry seems to be something like (this is added when configuring the build path via ui):

<classpathentry kind="con" path="org.eclipse.jdt.junit.JUNIT_CONTAINER/5">
<attributes>
<attribute name="test" value="true"/>
</attributes>
</classpathentry>

Probably needs to be done for all projects (didn't check, though ..)

edit:
let's update all the projects to use JUnit5