### 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
#include "export_plugin.h"
#include "gradle_export_util.h"
#include "core/config/project_settings.h"
#include "core/io/dir_access.h"
#include "core/io/file_access.h"
#include "core/io/image_loader.h"
#include "core/io/json.h"
#include "core/io/marshalls.h"
#include "core/version.h"
#include "drivers/png/png_driver_common.h"
#include "editor/editor_log.h"
#include "editor/editor_node.h"
#include "editor/editor_paths.h"
#include "editor/editor_scale.h"
#include "editor/editor_settings.h"
#include "main/splash.gen.h"
#include "platform/android/logo_svg.gen.h"
#include "platform/android/run_icon_svg.gen.h"
#include "modules/modules_enabled.gen.h" 
#ifdef MODULE_SVG_ENABLED
#include "modules/svg/image_loader_svg.h"
#endif
#include <string.h>
static const char *android_perms[] = {
	"ACCESS_CHECKIN_PROPERTIES",
	"ACCESS_COARSE_LOCATION",
	"ACCESS_FINE_LOCATION",