Add bitdepth to DisplayInfo

[riccardobl]

from forum post https://hub.jmonkeyengine.org/t/jme-3-10-0-beta1/49603/43?u=riccardoblb

In addition to the dimensions and refresh rate of each display mode, GLFW provides its bit depth. Would it be practical to add this information to com.jme3.system.DisplayInfo?

[hiSandog]

For DisplayInfo, “bitdepth” could mean several different values: color buffer bits, depth buffer bits, stencil bits, or display mode color depth. It would help to specify which one the API should expose and how it maps across LWJGL/platform backends. A test or sample output from the target platform would avoid ambiguity.