### 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
"ACCESS_LOCATION_EXTRA_COMMANDS",
	"ACCESS_MOCK_LOCATION",
	"ACCESS_NETWORK_STATE",
	"ACCESS_SURFACE_FLINGER",
	"ACCESS_WIFI_STATE",
	"ACCOUNT_MANAGER",
	"ADD_VOICEMAIL",
	"AUTHENTICATE_ACCOUNTS",
	"BATTERY_STATS",
	"BIND_ACCESSIBILITY_SERVICE",
	"BIND_APPWIDGET",
	"BIND_DEVICE_ADMIN",
	"BIND_INPUT_METHOD",
	"BIND_NFC_SERVICE",
	"BIND_NOTIFICATION_LISTENER_SERVICE",
	"BIND_PRINT_SERVICE",
	"BIND_REMOTEVIEWS",
	"BIND_TEXT_SERVICE",
	"BIND_VPN_SERVICE",
	"BIND_WALLPAPER",
	"BLUETOOTH",
	"BLUETOOTH_ADMIN",
	"BLUETOOTH_PRIVILEGED",
	"BRICK",
	"BROADCAST_PACKAGE_REMOVED",
	"BROADCAST_SMS",
	"BROADCAST_STICKY",
	"BROADCAST_WAP_PUSH",
	"CALL_PHONE",
	"CALL_PRIVILEGED",