feat(theming): Add a typesafe like API to get theming tokens CSS var names

### Feature Description

Currently there are Sass mixings that allow to, in a typesafe safe way, override theming tokens:

```
mat.snack-bar-overrides(....)
```

When saying typesafe, I mean that if a token is renamed or removed, the compiler will trigger an error. There are no equivalent to generating the CSS custom properties associated with these tokens.

### Use Case

Why this could help?

I have a component to show temporary messages, much like an snack-bar, but it isn't a snack bar, but it uses the same snack bar theming, same colors, for example. So this uses currently `--mat-snack-bar-` prefixed CSS variables. The problem is that migrating from version 19 up to 21, many of these variables names were renamed from `--mdc`- to `--mat`- prefixes thankfully automatically but it missed that for snack bars, the prefixes changed from snackbar to snack-bar.

If instead of using the var named directly we had some kind of:

```
mat.token-var(snack-bar, container-color, white)
```

to generate `var(--mat-snack-bar-container-color, white)` in a typesafe way, triggering an error if a bad component or token name is used, this could have avoided the missed rename.

ファイルもテストのエントリーポイントも指定されていません。まず、mat.snack-bar-overrides を含む既存の Sass override mixin と、ここで説明されている snack-bar の CSS custom-property の命名を調べてください。完了の条件は、トークン変数名を生成するための合意済みの typesafe API と、無効なコンポーネント名またはトークン名に対するカバレッジです。

索引モデルが issue の本文から書いたものです。