### 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
int bias = 0;
	while (ret == UNZ_OK) {
		unz_file_info info;
		memset(&info, 0, sizeof(info));
		char fname[16384];
		char extra[16384];
		ret = unzGetCurrentFileInfo(tmp_unaligned, &info, fname, 16384, extra, 16384 - ZIP_ALIGNMENT, nullptr, 0);
		if (ret != UNZ_OK) {
			break;
		}
		String file = String::utf8(fname);
		Vector<uint8_t> data;
		data.resize(info.compressed_size);
		
		int method, level;
		unzOpenCurrentFile2(tmp_unaligned, &method, &level, 1); 
		long file_offset = unzGetCurrentFileZStreamPos64(tmp_unaligned);
		unzReadCurrentFile(tmp_unaligned, data.ptrw(), data.size());
		unzCloseCurrentFile(tmp_unaligned);
		
		int padding = 0;
		if (!info.compression_method) {
			
			long new_offset = file_offset + bias;
			padding = (ZIP_ALIGNMENT - (new_offset % ZIP_ALIGNMENT)) % ZIP_ALIGNMENT;
		}
		memset(extra + info.size_file_extra, 0, padding);