Added implementations for eglQueryDisplayAttribEXT, eglQueryDeviceAttribEXT,
and eglQueryDeviceStringEXT.
Defined a new EGL_DEVICE_INDEX attribute for eglGetPlatformDisplay that uses
a device based on its index. This will allow us to test the case where
eglQueryDisplayAttribEXT returns an EGLDeviceEXT handle that libglvnd hasn't
seen before.
Updated egl_test_utils.c/h to include the new eglTestReturnDevice function.
Added functions to egl_test_utils.c/h to load each vendor's DummySetDeviceCount
function using dlopen+dlsym.
Added a test for EGL_EXT_device_enumeration and EGL_EXT_platform_device, plus
dispatching to an EGL extesnion function based on an EGLDeviceEXT handle.
Added two dummy libraries for EGL. They both use the same code, but each one
has a name string that can be used to check which vendor something is
dispatched to.
The dummy library is still incomplete, but more functions will be add later
along with more tests.
The test just creates an EGLDisplay using a dummy platform type, and then
checks to make sure that the display dispatches to the correct vendor library.
Also added a script to set up the test environment, and a file for common
functions and variables for EGL tests.
