### 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
String adb = get_adb_path();
		if (FileAccess::exists(adb)) {
			String devices;
			List<String> args;
			args.push_back("devices");
			int ec;
			OS::get_singleton()->execute(adb, args, &devices, &ec);
			Vector<String> ds = devices.split("\n");
			Vector<String> ldevices;
			for (int i = 1; i < ds.size(); i++) {
				String d = ds[i];
				int dpos = d.find("device");
				if (dpos == -1) {
					continue;
				}
				d = d.substr(0, dpos).strip_edges();
				ldevices.push_back(d);
			}
			MutexLock lock(ea->device_lock);
			bool different = false;
			if (ea->devices.size() != ldevices.size()) {
				different = true;
			} else {
				for (int i = 0; i < ea->devices.size(); i++) {
					if (ea->devices[i].id != ldevices[i]) {
						different = true;
						break;
					}
				}