Evas: adding image dump debug feature for wayland_egl backend

Evas: adding image dump debug feature for wayland_egl backend

Porting commit f10c108283d9b76708418ba172b9ff0b28a09cd6 to wayland
engine.

Added a feature to dump out a png image before calling SwapBuffers.
To turn on the feature, use the following env vars.

EVAS_GL_SWAP_BUFFER_DEBUG_DIR="dir_name" sets the name of the directory
that the files will be output to and enables the debug mode.

EVAS_GL_SWAP_BUFFER_DEBUG_ALWAYS=1 will enable the writing of the
files every frame.  This in effect turns on the swap_buffer_debug
variable, which can be set on or off in gdb for debugging.  This will
allow dumping of certain frames without having to dump out a ton of
files to track down one frame.