### 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
r_options->push_back(ExportOption(PropertyInfo(Variant::STRING, "keystore/release_password"), ""));
	r_options->push_back(ExportOption(PropertyInfo(Variant::INT, "version/code", PROPERTY_HINT_RANGE, "1,4096,1,or_greater"), 1));
	r_options->push_back(ExportOption(PropertyInfo(Variant::STRING, "version/name"), "1.0"));
	r_options->push_back(ExportOption(PropertyInfo(Variant::STRING, "package/unique_name", PROPERTY_HINT_PLACEHOLDER_TEXT, "ext.domain.name"), "org.godotengine.$genname"));
	r_options->push_back(ExportOption(PropertyInfo(Variant::STRING, "package/name", PROPERTY_HINT_PLACEHOLDER_TEXT, "Game Name [default if blank]"), ""));
	r_options->push_back(ExportOption(PropertyInfo(Variant::BOOL, "package/signed"), true));
	r_options->push_back(ExportOption(PropertyInfo(Variant::INT, "package/app_category", PROPERTY_HINT_ENUM, "Accessibility,Audio,Game,Image,Maps,News,Productivity,Social,Video"), APP_CATEGORY_GAME));
	r_options->push_back(ExportOption(PropertyInfo(Variant::BOOL, "package/retain_data_on_uninstall"), false));
	r_options->push_back(ExportOption(PropertyInfo(Variant::BOOL, "package/exclude_from_recents"), false));
	r_options->push_back(ExportOption(PropertyInfo(Variant::STRING, launcher_icon_option, PROPERTY_HINT_FILE, "*.png"), ""));
	r_options->push_back(ExportOption(PropertyInfo(Variant::STRING, launcher_adaptive_icon_foreground_option, PROPERTY_HINT_FILE, "*.png"), ""));
	r_options->push_back(ExportOption(PropertyInfo(Variant::STRING, launcher_adaptive_icon_background_option, PROPERTY_HINT_FILE, "*.png"), ""));
	r_options->push_back(ExportOption(PropertyInfo(Variant::BOOL, "graphics/opengl_debug"), false));
	r_options->push_back(ExportOption(PropertyInfo(Variant::INT, "xr_features/xr_mode", PROPERTY_HINT_ENUM, "Regular,OpenXR"), XR_MODE_REGULAR));
	r_options->push_back(ExportOption(PropertyInfo(Variant::INT, "xr_features/hand_tracking", PROPERTY_HINT_ENUM, "None,Optional,Required"), XR_HAND_TRACKING_NONE));
	r_options->push_back(ExportOption(PropertyInfo(Variant::INT, "xr_features/hand_tracking_frequency", PROPERTY_HINT_ENUM, "Low,High"), XR_HAND_TRACKING_FREQUENCY_LOW));
	r_options->push_back(ExportOption(PropertyInfo(Variant::INT, "xr_features/passthrough", PROPERTY_HINT_ENUM, "None,Optional,Required"), XR_PASSTHROUGH_NONE));
	r_options->push_back(ExportOption(PropertyInfo(Variant::BOOL, "screen/immersive_mode"), true));
	r_options->push_back(ExportOption(PropertyInfo(Variant::BOOL, "screen/support_small"), true));
	r_options->push_back(ExportOption(PropertyInfo(Variant::BOOL, "screen/support_normal"), true));
	r_options->push_back(ExportOption(PropertyInfo(Variant::BOOL, "screen/support_large"), true));
	r_options->push_back(ExportOption(PropertyInfo(Variant::BOOL, "screen/support_xlarge"), true));
	r_options->push_back(ExportOption(PropertyInfo(Variant::BOOL, "user_data_backup/allow"), false));
	r_options->push_back(ExportOption(PropertyInfo(Variant::STRING, "command_line/extra_args"), ""));
	r_options->push_back(ExportOption(PropertyInfo(Variant::BOOL, "apk_expansion/enable"), false));
	r_options->push_back(ExportOption(PropertyInfo(Variant::STRING, "apk_expansion/SALT"), ""));
	r_options->push_back(ExportOption(PropertyInfo(Variant::STRING, "apk_expansion/public_key", PROPERTY_HINT_MULTILINE_TEXT), ""));
	r_options->push_back(ExportOption(PropertyInfo(Variant::PACKED_STRING_ARRAY, "permissions/custom_permissions"), PackedStringArray()));
	const char **perms = android_perms;
	while (*perms) {