### 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
r_missing_templates = !has_export_templates;
		valid = dvalid || rvalid || has_export_templates;
		if (!valid) {
			err += template_err;
		}
	} else {
		bool installed_android_build_template = FileAccess::exists("res://android/build/build.gradle");
		if (!installed_android_build_template) {
			r_missing_templates = !exists_export_template("android_source.zip", &err);
			err += TTR("Android build template not installed in the project. Install it from the Project menu.") + "\n";
		} else {
			r_missing_templates = false;
		}
		valid = installed_android_build_template && !r_missing_templates;
	}
	
	String dk = p_preset->get("keystore/debug");
	String dk_user = p_preset->get("keystore/debug_user");
	String dk_password = p_preset->get("keystore/debug_password");
	if ((dk.is_empty() || dk_user.is_empty() || dk_password.is_empty()) && (!dk.is_empty() || !dk_user.is_empty() || !dk_password.is_empty())) {
		valid = false;
		err += TTR("Either Debug Keystore, Debug User AND Debug Password settings must be configured OR none of them.") + "\n";
	}
	if (!FileAccess::exists(dk)) {
		dk = EDITOR_GET("export/android/debug_keystore");
		if (!FileAccess::exists(dk)) {
			valid = false;
			err += TTR("Debug keystore not configured in the Editor Settings nor in the preset.") + "\n";
		}
	}