Add a test for switching between different contexts across multiple vendors.
The new test also checks libEGL's recovery when a vendor's eglMakeCurrent
fails.
The EGL dummy vendor will now keep track of the current context, so that we
can test whether eglMakeCurrent calls get passed through correctly.
Also added a command to force an eglMakeCurrent call to fail, and to fetch the
the current context from directly from a vendor library.
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 a test for eglGetProcAddress and dispatching for EGL and GL functions.
Added three EGL extension functions to the EGL dummy vendor, to test
dispatching extensions by display, device, and current context.
Added a simple implementation of eglCreateContext, eglDestroyContext, and
eglMakeCurrent, and glGetString.
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.