[WIP] FindOpenGL with GLESv2 and GLESv3
try to add GLESv2 and GLESv3 support to FindOpenGL module
later it should define additional targets OpenGL::GLES2 and OpenGL::GLES3 if available
as well as the variables OPENGL_GLES2_INCLUDE_DIRS, OPENGL_GLES3_INCLUDE_DIRS, OPENGL_gles2_LIBRARY, OPENGL_gles3_LIBRARY