### 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
if (!p_so.path.get_file().begins_with("lib")) {
		String err = "Android .so file names must start with \"lib\", but got: " + p_so.path;
		ERR_PRINT(err);
		return FAILED;
	}
	APKExportData *ed = static_cast<APKExportData *>(p_userdata);
	Vector<ABI> abis = get_abis();
	bool exported = false;
	for (int i = 0; i < p_so.tags.size(); ++i) {
		
		int abi_index = -1;
		for (int j = 0; j < abis.size(); ++j) {
			if (abis[j].abi == p_so.tags[i] || abis[j].arch == p_so.tags[i]) {
				abi_index = j;
				break;
			}
		}