Merge topic 'FindOpenGL-docs'

0496c430 FindOpenGL: Organize and format module documentation
Merge branch 'master' into next
FindOpenGL: Provide imported targets for GL and GLU

Create OpenGL::GL and OpenGL::GLU imported targets using the locations
found.
Merge topic 'FindOpenGL-target' into next

b7804cb6 FindOpenGL: Provide imported targets for GL and GLU