- moved a large portion of gl_textures.cpp into the main files for the implementing classes.

The old organization made sense when ZDoom still was a thing but now it'd be better if all pure data with no dependence on renderer implementation details was moved out.
A separation between GL2 and GL3+4 renderers looks to be inevitable and the more data is out of the renderer when that happens, the better.

src/gl/system/gl_framebuffer.cpp

@@ -98,7 +98,6 @@ OpenGLFrameBuffer::OpenGLFrameBuffer(void *hMonitor, int width, int height, int
 	mDebug = std::make_shared<FGLDebug>();
 	mDebug->Update();
 	gl_SetupMenu();
-	gl_GenerateGlobalBrightmapFromColormap();
 	DoSetGamma();
 }
 
@@ -454,7 +453,6 @@ void OpenGLFrameBuffer::GameRestart()
 	memcpy (SourcePalette, GPalette.BaseColors, sizeof(PalEntry)*256);
 	UpdatePalette ();
 	ScreenshotBuffer = NULL;
-	gl_GenerateGlobalBrightmapFromColormap();
 	GLRenderer->GetSpecialTextures();
 }