render: use internal_features to indicate EGL support

Instead of checking whether the wlr_egl dependencies are available
in the GLES2 code, introduce internal_features['egl'] and check
that field.

When updating the EGL dependency list, we no longer need to update
the GLES2 logic.

render/meson.build

@@ -20,6 +20,7 @@ if 'gles2' in renderers or 'auto' in renderers
 	if egl.found() and gbm.found()
 		wlr_deps += [egl, gbm]
 		wlr_files += files('egl.c')
+		internal_features += { 'egl': true }
 	endif
 	subdir('gles2')
 endif