### Godot version

3.5.1.stable, v4.0.beta.custom_build [0a87ead64]

### System information

Ubuntu 22.04.1

### Issue description

For example, if project has name "300spartans", we can't enter the "org.godotengine.300spartans" to "Unique Name" field. We get the error "Invalid package name: A digit cannot be the first character in a package segment". But , if we enter "org.godotengine.$genname", there will be no error message. When exporting, the name will be set as "org.godotengine.spartans" without "300" in beginning, but user will not be informed about it. I think, it is not very good. It may not be worth making changes to the source code, but mention it in the documentation.

### Steps to reproduce

See issue description.

### Minimal reproduction project

N/A
ERR_FAIL_INDEX_V(p_device, devices.size(), ERR_INVALID_PARAMETER);
	String can_export_error;
	bool can_export_missing_templates;
	if (!can_export(p_preset, can_export_error, can_export_missing_templates)) {
		add_message(EXPORT_MESSAGE_ERROR, TTR("Run"), can_export_error);
		return ERR_UNCONFIGURED;
	}
	MutexLock lock(device_lock);
	EditorProgress ep("run", vformat(TTR("Running on %s"), devices[p_device].name), 3);
	String adb = get_adb_path();
	
	if (ep.step(TTR("Exporting APK..."), 0)) {
		return ERR_SKIP;
	}
	const bool use_remote = (p_debug_flags & DEBUG_FLAG_REMOTE_DEBUG) || (p_debug_flags & DEBUG_FLAG_DUMB_CLIENT);
	const bool use_reverse = devices[p_device].api_level >= 21;
	if (use_reverse) {
		p_debug_flags |= DEBUG_FLAG_REMOTE_DEBUG_LOCALHOST;
	}
	String tmp_export_path = EditorPaths::get_singleton()->get_cache_dir().path_join("tmpexport." + uitos(OS::get_singleton()->get_unix_time()) + ".apk");