### 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
if (!p_check_executes) {
				break;
			}
			
			err = OS::get_singleton()->execute(apksigner_path, args, &output, &retval, false);
			if (err || retval) {
				failed = true;
			} else {
				break;
			}
		}
	}
	if (i == versions.size()) {
		if (failed) {
			print_error("All located 'apksigner' tools in " + build_tools_dir + " failed to execute");
			return "<FAILED>";
		} else {
			print_error("Unable to find the 'apksigner' tool.");
			return "";
		}
	}
	if (!found_target_sdk) {
		print_line("Could not find version of build tools that matches Target SDK, using " + version_to_use);
	} else if (failed && found_target_sdk) {
		print_line("Version of build tools that matches Target SDK failed to execute, using " + version_to_use);
	}
	return apksigner_path;
}
bool EditorExportPlatformAndroid::has_valid_export_configuration(const Ref<EditorExportPreset> &p_preset, String &r_error, bool &r_missing_templates) const {