### 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
String rk = p_preset->get("keystore/release");
	String rk_user = p_preset->get("keystore/release_user");
	String rk_password = p_preset->get("keystore/release_password");
	if ((rk.is_empty() || rk_user.is_empty() || rk_password.is_empty()) && (!rk.is_empty() || !rk_user.is_empty() || !rk_password.is_empty())) {
		valid = false;
		err += TTR("Either Release Keystore, Release User AND Release Password settings must be configured OR none of them.") + "\n";
	}
	if (!rk.is_empty() && !FileAccess::exists(rk)) {
		valid = false;
		err += TTR("Release keystore incorrectly configured in the export preset.") + "\n";
	}
	String sdk_path = EDITOR_GET("export/android/android_sdk_path");
	if (sdk_path.is_empty()) {
		err += TTR("A valid Android SDK path is required in Editor Settings.") + "\n";
		valid = false;
	} else {
		Error errn;
		
		Ref<DirAccess> da = DirAccess::open(sdk_path.path_join("platform-tools"), &errn);
		if (errn != OK) {
			err += TTR("Invalid Android SDK path in Editor Settings.");
			err += TTR("Missing 'platform-tools' directory!");
			err += "\n";
			valid = false;
		}
		
		String adb_path = get_adb_path();
		if (!FileAccess::exists(adb_path)) {
			err += TTR("Unable to find Android SDK platform-tools' adb command.");
			err += TTR("Please check in the Android SDK directory specified in Editor Settings.");