JavaFX calls unknown class

[taylor.smock]

What steps will reproduce the problem?

1. Install a Mapillary plugin snapshot (I used the version from ​https://gitlab.com/gokaart/josm-mapillary-plugin/-/jobs/500339283 -- download job artifacts, open zip, go to build/dist and copy the jar file to the JOSM plugins directory)
2. Install the appropriate javafx plugin (crashes on Windows and Mac, Linux not yet tested)
3. Restart, if necessary. I've only been able to reproduce using OpenWebStart (I haven't tested IcedTea yet). Calling the .jar file from the CLI with java -jar works (java -version indicates AdoptOpenJDK 11.0.6, in this case).
4. Download an area
5. If not already shown, show the Mapillary Filter toggle dialog (it uses JavaFX for date pickers)

What is the expected result?

No crash. :)

What happens instead?

Crash. :(

Please provide any additional information below. Attach a screenshot if possible.

Occurs with 11.0.6 Zulu Community Edition and 11.0.6 AdoptOpenJDK.

Relative:URL: ^/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2020-04-06 02:17:07 +0200 (Mon, 06 Apr 2020)
Revision:16239
Build-Date:2020-04-06 00:18:43
URL:https://josm.openstreetmap.de/svn/trunk

Identification: JOSM/1.5 (16239 en) Windows 10 64-Bit
OS Build number: Windows 10 Home 1803 (17134)
Memory Usage: 551 MB / 2048 MB (322 MB allocated, but free)
Java version: 11.0.6+10-LTS, Azul Systems, Inc., OpenJDK 64-Bit Server VM
Screen: \Display0 3840x2160, \Display1 3840x2160
Maximum Screen Size: 3840x2160
VM arguments: [-Djava.util.Arrays.useLegacyMergeSort=true, --add-reads=java.base=ALL-UNNAMED,java.desktop, --add-reads=java.desktop=ALL-UNNAMED,java.naming, --add-reads=java.naming=ALL-UNNAMED,java.desktop, --add-exports=java.desktop/sun.awt=ALL-UNNAMED,java.desktop, --add-exports=java.desktop/javax.jnlp=ALL-UNNAMED,java.desktop, --add-exports=java.base/com.sun.net.ssl.internal.ssl=ALL-UNNAMED,java.desktop, --add-exports=java.base/sun.net.www.protocol.jar=ALL-UNNAMED,java.desktop, --add-exports=java.base/sun.security.action=ALL-UNNAMED,java.desktop, --add-exports=java.base/sun.security.provider=ALL-UNNAMED,java.desktop, --add-exports=java.base/sun.security.util=ALL-UNNAMED,java.desktop, --add-exports=java.base/sun.security.validator=ALL-UNNAMED,java.desktop, --add-exports=java.base/sun.security.x509=ALL-UNNAMED,java.desktop, --add-exports=java.base/jdk.internal.util.jar=ALL-UNNAMED,java.desktop, --add-exports=java.base/sun.net.www.protocol.http=ALL-UNNAMED,java.desktop, --add-exports=java.desktop/sun.awt.X11=ALL-UNNAMED,java.desktop, --add-exports=java.desktop/sun.applet=ALL-UNNAMED,java.desktop, --add-exports=java.desktop/sun.applet=ALL-UNNAMED,jdk.jsobject, --add-exports=java.naming/com.sun.jndi.toolkit.url=ALL-UNNAMED,java.desktop]
Dataset consistency test: No problems found

Plugins:
+ Mapillary (1.5.20-83-g53ef3bd)
+ apache-commons (35362)
+ apache-http (35092)
+ javafx-windows (35375)
+ jna (35092)

Last errors/warnings:
- E: Region [TMS_BLOCK_v2] Failure getting from disk, key = OpenStreetMap Carto (Standard):https://{switch:a,b,c}.tile.openstreetmap.org/{zoom}/{x}/{y}.png/15/6501/12515
- E: Region [TMS_BLOCK_v2] Failure getting from disk, key = OpenStreetMap Carto (Standard):https://{switch:a,b,c}.tile.openstreetmap.org/{zoom}/{x}/{y}.png/15/6504/12516
- E: Region [TMS_BLOCK_v2] Failure getting from disk, key = OpenStreetMap Carto (Standard):https://{switch:a,b,c}.tile.openstreetmap.org/{zoom}/{x}/{y}.png/15/6503/12515
- E: Region [TMS_BLOCK_v2] Failure getting from disk, key = OpenStreetMap Carto (Standard):https://{switch:a,b,c}.tile.openstreetmap.org/{zoom}/{x}/{y}.png/15/6501/12514
- E: Handled by bug report queue: java.lang.NoClassDefFoundError: jdk/swing/interop/SwingInterOpUtils. Cause: java.lang.ClassNotFoundException: jdk.swing.interop.SwingInterOpUtils
- E: Handled by bug report queue: java.lang.NoClassDefFoundError: jdk/swing/interop/SwingInterOpUtils
- E: Handled by bug report queue: java.lang.NoClassDefFoundError: jdk/swing/interop/SwingInterOpUtils
- E: Handled by bug report queue: java.lang.NoClassDefFoundError: jdk/swing/interop/SwingInterOpUtils
- E: Handled by bug report queue: java.lang.NoClassDefFoundError: jdk/swing/interop/SwingInterOpUtils
- W: Warning - <html>JOSM could not find information about the following plugins:<ul><li>apache-commons</li><li>Mapillary</li><li>javafx-windows</li><li>jna</li><li>apache-http</li></ul>The plugins are not going to be loaded.</html>


=== REPORTED CRASH DATA ===
BugReportExceptionHandler#handleException:
No data collected.

Warning issued by: BugReportExceptionHandler#handleException

=== STACK TRACE ===
Thread: JavaFX Application Thread (144) of JOSM
java.lang.NoClassDefFoundError: jdk/swing/interop/SwingInterOpUtils
	at com.sun.javafx.embed.swing.newimpl.JFXPanelInteropN.postEvent(JFXPanelInteropN.java:36)
	at javafx.embed.swing.JFXPanel.invokeOnClientEDT(JFXPanel.java:930)
	at javafx.embed.swing.JFXPanel$HostContainer.setEmbeddedScene(JFXPanel.java:972)
	at com.sun.javafx.tk.quantum.EmbeddedScene.setStage(EmbeddedScene.java:122)
	at com.sun.javafx.tk.quantum.GlassStage.setScene(GlassStage.java:94)
	at com.sun.javafx.tk.quantum.EmbeddedStage.setScene(EmbeddedStage.java:62)
	at javafx.stage.Window$12.invalidated(Window.java:1085)
	at javafx.beans.property.BooleanPropertyBase.markInvalid(BooleanPropertyBase.java:110)
	at javafx.beans.property.BooleanPropertyBase.set(BooleanPropertyBase.java:145)
	at javafx.stage.Window.setShowing(Window.java:1174)
	at javafx.stage.Window.show(Window.java:1189)
	at com.sun.javafx.stage.EmbeddedWindow.show(EmbeddedWindow.java:71)
	at javafx.embed.swing.JFXPanel.setSceneImpl(JFXPanel.java:326)
	at javafx.embed.swing.JFXPanel.setScene(JFXPanel.java:296)
	at org.openstreetmap.josm.plugins.javafx.gui.JavaFxWrapper.initFX(JavaFxWrapper.java:71)
	at com.sun.javafx.application.PlatformImpl.lambda$runLater$10(PlatformImpl.java:428)
	at java.base/java.security.AccessController.doPrivileged(Native Method)
	at com.sun.javafx.application.PlatformImpl.lambda$runLater$11(PlatformImpl.java:427)
	at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
	at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
	at com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:174)
	at java.base/java.lang.Thread.run(Thread.java:834)
Caused by: java.lang.ClassNotFoundException: jdk.swing.interop.SwingInterOpUtils
	at java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:471)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:588)
	at org.openstreetmap.josm.plugins.PluginClassLoader.loadClass(PluginClassLoader.java:73)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521)
	... 22 more

See #17858