Fixes #1241 - Add a convenient Graphics Debug Option for the AppSettings

[MeFisto94]

Same policy here, especially since nobody commented on #1241 - Going to merge in 7 days.
I've also fixed a javadoc warning in the surrounding code, sorry for that :D

[stephengold]

This sounds like a great idea, but when I add setGraphicsDebug(true) to HelloJME3 and run it, it crashes quickly with a RendererException:

Jan 26, 2020 11:58:09 PM com.jme3.app.LegacyApplication handleError
SEVERE: Uncaught exception thrown in Thread[jME3 Main,5,main]
com.jme3.renderer.RendererException: Image format 'ABGR8' is unsupported by the video hardware.
	at com.jme3.renderer.opengl.TextureUtil.getImageFormatWithError(TextureUtil.java:102)
	at com.jme3.renderer.opengl.TextureUtil.uploadTexture(TextureUtil.java:252)
	at com.jme3.renderer.opengl.GLRenderer.updateTexImageData(GLRenderer.java:2498)
	at com.jme3.renderer.opengl.GLRenderer.setTexture(GLRenderer.java:2536)
	at com.jme3.material.Material.updateShaderMaterialParameters(Material.java:845)
	at com.jme3.material.Material.render(Material.java:1020)
	at com.jme3.renderer.RenderManager.renderGeometry(RenderManager.java:614)
	at com.jme3.renderer.queue.RenderQueue.renderGeometryList(RenderQueue.java:266)
	at com.jme3.renderer.queue.RenderQueue.renderQueue(RenderQueue.java:302)
	at com.jme3.renderer.RenderManager.renderViewPortQueues(RenderManager.java:905)
	at com.jme3.renderer.RenderManager.flushQueue(RenderManager.java:779)
	at com.jme3.renderer.RenderManager.renderViewPort(RenderManager.java:1108)
	at com.jme3.renderer.RenderManager.render(RenderManager.java:1166)
	at com.jme3.app.SimpleApplication.update(SimpleApplication.java:272)
	at com.jme3.system.lwjgl.LwjglAbstractDisplay.runLoop(LwjglAbstractDisplay.java:151)
	at com.jme3.system.lwjgl.LwjglDisplay.runLoop(LwjglDisplay.java:197)
	at com.jme3.system.lwjgl.LwjglAbstractDisplay.run(LwjglAbstractDisplay.java:232)
	at java.lang.Thread.run(Thread.java:748)

Perhaps address the errors before adding this feature?

[MeFisto94]

Yes, this is "expected" and one of the reasons I want to push for adding GraphicsDebug:
Essentially everything needs to be run with GraphicsDebug as we otherwise ignore so many problems.
Another one happens when trying to run openGL 3.2 within loading the extensions (GL_INVALID_ENUM), which we otherwise silently ignore.

In the following days I will extend my testing, so we can find a few of these cases, but they might still pop up for users from time to time then.

Regarding said exception: https://github.com/jMonkeyEngine/jmonkeyengine/blob/master/jme3-jogl/src/main/java/com/jme3/renderer/jogl/TextureUtil.java#L172
This could stem from some different variant of #1243
Can you run glxinfo and see if GL_EXT_abgr is present? For me it certainly was.
Another question would be why abgrToRgbaConversionEnabled isn't enabled. It would bypass this problem by converting the files, which is slow but works on unsupported hardware. See here

Oh and another question is if this code is basically the same for lwjgl, I only stumbled over jogl during a short web search.

We might spin this of into a separate issue actually

[stephengold]

I agree that separate issues are warranted for any errors encountered when the debug option is enabled.

[stephengold]

I've opened issue #1272 and will integrate this PR promptly to support additional testing.

[MeFisto94]

Actually forgot to mention: @mitm001 might want to check if the wiki mentions GraphicsDebug at all and if not, could maybe incooperate it into the "debugging" section :)