### 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
String p = props[j];
							p = p.replace("]: ", "=");
							p = p.replace("[", "");
							p = p.replace("]", "");
							if (p.begins_with("ro.product.model=")) {
								device = p.get_slice("=", 1).strip_edges();
							} else if (p.begins_with("ro.product.brand=")) {
								vendor = p.get_slice("=", 1).strip_edges().capitalize();
							} else if (p.begins_with("ro.build.display.id=")) {
								d.description += "Build: " + p.get_slice("=", 1).strip_edges() + "\n";
							} else if (p.begins_with("ro.build.version.release=")) {
								d.description += "Release: " + p.get_slice("=", 1).strip_edges() + "\n";
							} else if (p.begins_with("ro.build.version.sdk=")) {
								d.api_level = p.get_slice("=", 1).to_int();
							} else if (p.begins_with("ro.product.cpu.abi=")) {
								d.description += "CPU: " + p.get_slice("=", 1).strip_edges() + "\n";
							} else if (p.begins_with("ro.product.manufacturer=")) {
								d.description += "Manufacturer: " + p.get_slice("=", 1).strip_edges() + "\n";
							} else if (p.begins_with("ro.board.platform=")) {
								d.description += "Chipset: " + p.get_slice("=", 1).strip_edges() + "\n";
							} else if (p.begins_with("ro.opengles.version=")) {
								uint32_t opengl = p.get_slice("=", 1).to_int();
								d.description += "OpenGL: " + itos(opengl >> 16) + "." + itos((opengl >> 8) & 0xFF) + "." + itos((opengl)&0xFF) + "\n";
							}
						}
						d.name = vendor + " " + device;
						if (device.is_empty()) {
							continue;