feat: extended FAB

# Feature Request

**Ionic version:**
[x] **5.2.1**

**Describe the Feature Request**
Ion Fab Expanded button: As per google material design, there is an option to add an expanded version of ion-fab. Check this link to see more [https://material.io/components/buttons-floating-action-button#extended-fab](https://material.io/components/buttons-floating-action-button#extended-fab)

**Describe Preferred Solution**
Currently there is no option in the framework for us to use the expanded version. It might be activated using a directive:
```

Compose

```
**Additional Context**
Gmail App:
[Screenshot](https://cdn.vox-cdn.com/thumbor/PzhykRfqcf_gRZnLtKrzLHxi9-I=/0x1498:1080x2160/1200x800/filters:focal(756x1929:928x2101)/cdn.vox-cdn.com/uploads/chorus_image/image/66898321/Screenshot_20200605_092605.0.png)

The request targets the ion-fab-button component and proposes an expanded usage with an icon and Compose label. Start by locating that component and its existing tests; done means the expanded FAB is supported consistently with the linked Material Design example and the proposed markup is covered by tests.

索引モデルが issue の本文から書いたものです。