stb_image.h path inclusion for using shared libraries

[Kreijstal]

the file src/webots/nodes/WbBackground.cpp uses stb_image.h instead of stb/stb_image.h this is if you package webots for distros where stb is provided :)
Overv/VulkanTutorial#251

also in file
src/controller/c/g_image.c

[Kreijstal]

One way to solve this is to create another directory on stb, or to change the stb import, which one do you think is more appropiate?

[omichel]

I would prefer to avoid creating some webots/src/stb/stb folder as it doesn't look very nice.

[Kreijstal]

we could also change the line in src/webots/Makefile of
STB_INCLUDE = -isystem $(WEBOTS_PATH)/src/stb
to STB_INCLUDE = -isystem $(WEBOTS_PATH)/src

but I think the nested stb is nicer, the reason is that on 2018 there was no package in most systems, but now there is so systems like windows (msys2) you can simply just use mingw-w64-x86_64-stb, on ubuntu/debian there is libstb and libstb-dev
and it compiles as it is without subcloning just using make :) (of course there is mingw-w64-x86_64-glm too)

[omichel]

OK, then we should probably remove this stb folder and use the one from the system. We should add it to the dependencies, so that the right version gets installed:

• https://github.com/cyberbotics/webots/blob/master/scripts/install/msys64_installer.sh
• https://github.com/cyberbotics/webots/blob/master/scripts/install/linux_compilation_dependencies.sh
• https://github.com/cyberbotics/webots/wiki/macOS-installation