Integrate libdisplay-info (optional at first)

This series prepares libweston/DRM-backend to use libdisplay-info for parsing EDID. Libdisplay-info will be used if it was found during build. There is also a Meson sub-project for fallback.

The old ad hoc EDID parsing code is still left in, to be used when libdisplay-info is not available. The old code is intended to be removed in the future and make libdisplay-info a hard dependency in DRM-backend.

The old ad hoc parser will no longer pretend that all monitors are capable of all HDR modes. This makes libdisplay-info mandatory for HDR testing already. In the future, libdisplay-info will be used to extract HDR information from EDID, and the ad hoc parser will not get code for that.

Considerations for merging during the release cycle: no ABI is broken, I think the changes are low-risk, and even though a new dependency is introduced, it is optional and automatic. Therefore I think this is suitable for landing before the beta release.

Libdisplay-info does produce potentially different strings than the old ad hoc code.

Draft until I have fixed CI failures.

compositor/main.c

@@ -1401,6 +1401,10 @@ wet_output_set_eotf_mode(struct weston_output *output,
 	if ((weston_output_get_supported_eotf_modes(output) & eotf_mode) == 0) {
 		weston_log("Error: output '%s' does not support EOTF mode %s.\n",
 			   output->name, str);
+#if !HAVE_LIBDISPLAY_INFO
+		weston_log_continue(STAMP_SPACE "Weston was built without libdisplay-info, "
+				    "so HDR capabilities cannot be detected.\n");
+#endif
 		free(str);
 		return -1;
 	}