fix(i18n): add i18n support for steve & alex option in offline skin pane (#3630)

Some Slavic Minecraft communities have translated Steve and Alex,
such as Russian and Ukrainian. They need a translation.

ref:
- https://ru.minecraft.wiki/w/%D0%A1%D0%BA%D0%B8%D0%BD
- https://uk.minecraft.wiki/w/%D0%A1%D0%BA%D1%96%D0%BD

HMCL/src/main/resources/assets/lang/I18N_zh_CN.properties

@@ -157,12 +157,14 @@ account.skin.file=皮肤图片文件
 account.skin.model=模型
 account.skin.model.default=宽型
 account.skin.model.slim=纤细
+account.skin.type.alex=Alex
 account.skin.type.csl_api=Blessing Skin 服务器
 account.skin.type.csl_api.location=服务器地址
 account.skin.type.csl_api.location.hint=CustomSkinAPI 地址
 account.skin.type.little_skin=LittleSkin 皮肤站
 account.skin.type.little_skin.hint=你需要在皮肤站中创建并使用和该离线账户同名的角色，此时离线账户皮肤将显示为皮肤站上对应角色所设置的皮肤。\n你可以点击右上角帮助按钮进行求助。
 account.skin.type.local_file=本地皮肤图片文件
+account.skin.type.steve=Steve
 account.skin.upload=上传/编辑皮肤
 account.skin.upload.failed=皮肤上传失败
 account.skin.invalid_skin=无法识别的皮肤文件