Switch to using EGL

[haudren]

Replace GLFW backend with EGL. GLFW has two disadvantages:

• It's an external dependency
• It requires an active display and window manager

On the other hand, this PR switches to EGL which is built-in to modern OpenGL, and does not require a window manager.

Please ignore all changes related to egl.{c,h}, gl.{c,h} and glad.{c,h} as those are auto-generated via GLAD

To test:

cd gl_depth_sim
mkdir build
cd build 
cmake ..
make
#first render
./depth_sim_example /path_to_some_mesh
cp img.png headful.png
unset DISPLAY
# Headless rendering
./depth_sim_example /path_to_some_mesh
# Compare both images