### 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
#ifndef ANDROID_EXPORT_PLUGIN_H
#define ANDROID_EXPORT_PLUGIN_H
#include "godot_plugin_config.h"
#include "core/io/zip_io.h"
#include "core/os/os.h"
#include "editor/export/editor_export_platform.h"
const String SPLASH_CONFIG_XML_CONTENT = R"SPLASH(<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@drawable/splash_bg_color" />
    <item>
        <bitmap
                android:gravity="center"
                android:filter="%s"
                android:src="@drawable/splash" />
    </item>
</layer-list>
)SPLASH";
struct LauncherIcon {
	const char *export_path;
	int dimensions = 0;
};
class EditorExportPlatformAndroid : public EditorExportPlatform {