### 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
chars += 2;
		for (int j = 0; j < s.length(); j++) {
			encode_uint16(s[j], chars);
			chars += 2;
		}
		encode_uint16(0, chars);
		chars += 2;
	}
	
	while (ret.size() % 4) {
		ret.push_back(0);
	}
	
	encode_uint32(string_flags & ~0x100, &ret.write[28]);
	
	encode_uint32(ret.size() - 12, &ret.write[16]);
	
	int rest_from = 12 + string_block_len;
	int rest_to = ret.size();
	int rest_len = (r_manifest.size() - rest_from);
	ret.resize(ret.size() + (r_manifest.size() - rest_from));
	for (int i = 0; i < rest_len; i++) {
		ret.write[rest_to + i] = r_manifest[rest_from + i];
	}
	
	encode_uint32(ret.size(), &ret.write[4]);
	r_manifest = ret;
	
}
void EditorExportPlatformAndroid::_load_image_data(const Ref<Image> &p_splash_image, Vector<uint8_t> &p_data) {