[Story] Show RTE options when highlighting a text in the composer

### Story

As a user that has written text in the composer and is highlighting some of the text we want to access the formatting options to show so that I can easily format the text.

## Acceptance criteria
- Add one new menu item to be shown when the user highlights text ("Format").
- The menu item should not show when the text formatting menu is already open.

## Scope

```[tasklist]
### Android
- [ ] Expose ability to customise selection menu in Rich Text Editor
- [ ] Add menu item that when tapped, starts the
- [ ] Verified with build in screen reader
```

```[tasklist]
### iOS
- [ ] Expose ability to customise selection menu in Rich Text Editor
- [ ] Add menu item that when tapped, starts the
- [ ] Verified with build in screen reader
```

```[tasklist]
### Web
- [ ] Verified with build in screen reader
```

- [ ] QA signoff on completion
- [ ] Design signoff on completion
- [ ] Product signoff on completion

## Stretch goals
None at this time

## Out of scope
-

No files or tests are named. Start by locating the Android and iOS Rich Text Editor selection-menu implementations, then verify how the existing formatting menu is opened. Done means a "Format" item appears for highlighted text only when that formatting menu is closed, with screen-reader verification and the listed QA, design, and product signoffs.

Written by the indexing model from the issue text.