Figure out why appbundler breaks OpenGL when built on Catalina and later

Created by: benfry

As seen in #249, Export to Application was broken in alpha 5 and beta 1. This was after the native code for JavaApplicationStub was built on Catalina or Big Sur. Using a Mojave machine got things working again.

As can be seen in #249, it seems to be a threading issue (GL seems to be running on the wrong thread). I suspect there's something bad in our code, and that the Catalina/Big Sur change is just revealing it. Can someone help us find it?

It's also not a problem in our fork of appbundler: recompiling with the latest upstream source (on Big Sur) led to the same crash.

It's also possible that the macOS SDK has had a change with with regards to app threads. The -XstartOnFirstThread [parameter](https://www.google.com/search?q='Reference to deleted milestone 22'-xstartonfirstthread%22) is a very real thing on macOS, where app threads are Thinked Differently than on other platforms.

To dig into this issue:

cd build/macosx/appbundler
ant
cd ../..
ant run

Then open an OpenGL sketch, Export to Application, and watch as it crashes on startup. Behold the confusing stack trace. Or perhaps if you have more macOS development experience, become invigorated by the challenge of un-mucking this Java/macOS integration.

(Edited for clarification)

Start in build/macosx/appbundler and run ant, then from the parent build directory run ant run. Open an OpenGL sketch and use Export to Application to reproduce the startup crash and inspect its stack trace. Done means exported OpenGL applications start without the Catalina or Big Sur threading-related crash.