bug(cdk/scrolling): The append only mode assumes that scrolling starts at zero and therefore calculates renderedRange incorrectly

#### Reproduction

Steps to reproduce:
1. Create a virtual scroll container with `appendOnly`
2. Load the virtual scroll container and don't load it from the top
3. The `renderedRange` is wrongly calculated/set

#### Expected Behavior

A virtual scroll container can be loaded at any position without `renderedRange` being set incorrectly.

#### Actual Behavior

The `renderedRange` was set incorrectly once the virtual scroll container was loaded not at the top. I archived this behaviour via the following CSS setting.

```
[cdk-virtual-scroll-viewport] {
overflow-anchor: none;
}
```

#### A possible solution

I was able to solve this issue by overriding the following code at [virtual-scroll-viewport.ts#L292](https://github.com/angular/components/blob/6076801883194f263a5c692797ffc863a8de9771/src/cdk/scrolling/virtual-scroll-viewport.ts#L292)

```diff
if (this.appendOnly) {
- range = {start: 0, end: Math.max(this._renderedRange.end, range.end)};
+ range = {start: Math.min(this._renderedRange.start, range.start), end: Math.max(this._renderedRange.end, range.end)};
}
```

I am not sure if I am missing something. For this reason, I have just opened an issue and no pull request for now.

#### Environment

- Angular: 12.2.5
- CDK/Material: 12.2.5
- Browser(s): Chrome
- Operating System (e.g. Windows, macOS, Ubuntu): macOS

src/cdk/scrolling/virtual-scroll-viewport.ts の 292 行目付近にある appendOnly の範囲計算から始め、ゼロ以外の位置で読み込まれた仮想スクロールコンテナで問題を再現します。renderedRange が開始位置をゼロと仮定せず、最初に読み込まれた範囲を保持することを確認します。このケースで appendOnly が正しく動作すれば作業は完了です。

索引モデルが issue の本文から書いたものです。