### 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 (file.ends_with(".png") && file.contains("mipmap")) {
			for (int i = 0; i < icon_densities_count; ++i) {
				if (main_image.is_valid() && !main_image->is_empty()) {
					if (file == launcher_icons[i].export_path) {
						_process_launcher_icons(file, main_image, launcher_icons[i].dimensions, data);
					}
				}
				if (foreground.is_valid() && !foreground->is_empty()) {
					if (file == launcher_adaptive_icon_foregrounds[i].export_path) {
						_process_launcher_icons(file, foreground, launcher_adaptive_icon_foregrounds[i].dimensions, data);
					}
				}
				if (background.is_valid() && !background->is_empty()) {
					if (file == launcher_adaptive_icon_backgrounds[i].export_path) {
						_process_launcher_icons(file, background, launcher_adaptive_icon_backgrounds[i].dimensions, data);
					}
				}
			}
		}
		if (file.ends_with(".so")) {
			bool enabled = false;
			for (int i = 0; i < enabled_abis.size(); ++i) {
				if (file.begins_with("lib/" + enabled_abis[i].abi + "/")) {
					invalid_abis.erase(enabled_abis[i]);
					enabled = true;
					break;
				}
			}
			if (!enabled) {
				skip = true;