### 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
"READ_SOCIAL_STREAM",
	"READ_SYNC_SETTINGS",
	"READ_SYNC_STATS",
	"READ_USER_DICTIONARY",
	"REBOOT",
	"RECEIVE_BOOT_COMPLETED",
	"RECEIVE_MMS",
	"RECEIVE_SMS",
	"RECEIVE_WAP_PUSH",
	"RECORD_AUDIO",
	"REORDER_TASKS",
	"RESTART_PACKAGES",
	"SEND_RESPOND_VIA_MESSAGE",
	"SEND_SMS",
	"SET_ACTIVITY_WATCHER",
	"SET_ALARM",
	"SET_ALWAYS_FINISH",
	"SET_ANIMATION_SCALE",
	"SET_DEBUG_APP",
	"SET_ORIENTATION",
	"SET_POINTER_SPEED",
	"SET_PREFERRED_APPLICATIONS",
	"SET_PROCESS_LIMIT",
	"SET_TIME",
	"SET_TIME_ZONE",
	"SET_WALLPAPER",
	"SET_WALLPAPER_HINTS",
	"SIGNAL_PERSISTENT_PROCESSES",
	"STATUS_BAR",
	"SUBSCRIBED_FEEDS_READ",