### 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
offset += 2;
		if (len & 0x8000) {
			len &= 0x7FFF;
			len = (len << 16) + decode_uint16(&p_bytes[offset]);
			offset += 2;
		}
	}
	if (p_utf8) {
		Vector<uint8_t> str8;
		str8.resize(len + 1);
		for (uint32_t i = 0; i < len; i++) {
			str8.write[i] = p_bytes[offset + i];
		}
		str8.write[len] = 0;
		String str;
		str.parse_utf8((const char *)str8.ptr());
		return str;
	} else {
		String str;
		for (uint32_t i = 0; i < len; i++) {
			char32_t c = decode_uint16(&p_bytes[offset + i * 2]);
			if (c == 0) {
				break;
			}
			str += String::chr(c);
		}
		return str;
	}
}
void EditorExportPlatformAndroid::_fix_resources(const Ref<EditorExportPreset> &p_preset, Vector<uint8_t> &r_manifest) {