feat(theming): Mixins for reading component style tokens

### Feature Description

Mixins to get values from a component theme that takes a token as parameter, for example:
```
p {
color: @include mat.button-get(text-label-text-color);
}
```
it would generate:
```
p {
color: var(--mdc-outlined-button-label-text-color, var(--mat-sys-primary)); // <== Actual value used for text-button
}
```

Ideally, we would have as many mixins as there are components (+core) and we could use the same tokens as the `mat.-overrides` mixins.

> The `mat.-get` mixin name is a proposal, open to suggestions.

### Use Case

I have a custom component and I want to apply the same style as a material component. I also want to make sure that they are always in sync when I change my theme.

For example, I want to have a text `

` with the same font color as my `mat-button` next to it.

For now, I need to rely on private CSS variables to do that, which is not ideal for maintainability.

この issue ではファイルやテストが指定されていません。まず既存の `mat.-overrides` mixin を読み、そこにあるトークンを提案されている `mat.-get` API と比較してください。目的の mixin の範囲と命名が定義され、ユーザーがカスタムスタイル用にコンポーネントのテーマトークンの値を読み取れるようになれば完了です。

索引モデルが issue の本文から書いたものです。