Replace favicon.ico in favor of png in src/assets

### Bug Report or Feature Request (mark with an `x`)
```
- [ ] bug report -> please search issues before submitting
- [x] feature request
```

### Area
```
- [ ] devkit
- [x] schematics
```

### Desired functionality
favicon.ico is outdated and obsolete relic from the 90s. Browsers for the past 2decades have supported png favicons. Additionally, while it's fairly easy now to generate a favicon.ico, it's just not needed or used anymore.

There's no reason imo to include favicon.ico, even for "compatibility". Removing the favicon.ico will also remove the entries needed in angular.json and remove the only asset stored outside of src/assets.

It should be replaced in favor of modern favicon methods. PWAs should use manifest.json

```



```
Note: svg doesn't have full browser support.

We haven't needed favicon.ico in years, but it's still widely used and implemented, even though all browsers support modern methods.

首先追踪创建 favicon 的 schematic 文件以及 angular.json 中的相关条目，然后检查 src/assets 中的当前图标。确认生成的应用程序应包含哪些现代 PNG 或基于 manifest 的文件，移除过时的 favicon.ico 引用，并在相关 schematic 测试覆盖生成的 asset 时更新这些测试。

由索引模型根据 Issue 内容生成。