feat(CdkMenu): Option to disable typeahead in CdkMenu

### Feature Description

We would like to add an option in the `CdkMenu` to disable the integrated TypeAhead feature.

Currently, the menu activates the TypeAhead for its `FocusKeyManager` automatically:
https://github.com/angular/components/blob/e91d5091bbf3d44cc168be458269d260a0c22c27/src/cdk/menu/menu-base.ts#L175

The proposal would be to add an input like `cdkMenuTypeAhead: boolean` which defaults to true but can be used to skip the TypeAhead activation:
```ts
this.keyManager = new FocusKeyManager(this.items).withWrap().withHomeAndEnd();
if (this.cdkMenuTypeAhead) {
this.keyManager = this.keyManager.withTypeAhead()
}
```

#### Alternative

An alternative approach might be a combination of the following features, so the described use case can be accomplished by the `CdkMenu` itself.
1. Make the current search term (`_pressedLetters`) publicly available, so it can be displayed.
2. Two variants to extend the current search logic:
2.a Add a secondary `includes` search to the current `startsWith`.
2.b Make the search logic customizable with configurable predicate function.

### Use Case

The use case is a custom search feature for our menus, which conflicts with the integrated TypeAhead.
We want to display the current search term and search by `startsWith` & `includes`.

 

***

**🗨 I would appreciate some feedback, if this feature has a chance of being accepted. Then I can prepare a PR for this.**

src/cdk/menu/menu-base.ts の、リンクされた行付近にある FocusKeyManager のセットアップから開始し、CdkMenu の入力がどのように宣言され、typeahead がどのように有効化されるかを追ってください。メニューで typeahead を無効にでき、現在のデフォルト動作を維持できれば変更は完了です。可能であれば既存のメニューテストを確認して、両方の経路を検証してください。

索引モデルが issue の本文から書いたものです。