### 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
"INSTALL_PACKAGES",
	"INSTALL_SHORTCUT",
	"INTERNAL_SYSTEM_WINDOW",
	"INTERNET",
	"KILL_BACKGROUND_PROCESSES",
	"LOCATION_HARDWARE",
	"MANAGE_ACCOUNTS",
	"MANAGE_APP_TOKENS",
	"MANAGE_DOCUMENTS",
	"MANAGE_EXTERNAL_STORAGE",
	"MASTER_CLEAR",
	"MEDIA_CONTENT_CONTROL",
	"MODIFY_AUDIO_SETTINGS",
	"MODIFY_PHONE_STATE",
	"MOUNT_FORMAT_FILESYSTEMS",
	"MOUNT_UNMOUNT_FILESYSTEMS",
	"NFC",
	"PERSISTENT_ACTIVITY",
	"PROCESS_OUTGOING_CALLS",
	"READ_CALENDAR",
	"READ_CALL_LOG",
	"READ_CONTACTS",
	"READ_EXTERNAL_STORAGE",
	"READ_FRAME_BUFFER",
	"READ_HISTORY_BOOKMARKS",
	"READ_INPUT_STATE",
	"READ_LOGS",
	"READ_PHONE_STATE",
	"READ_PROFILE",
	"READ_SMS",