Expose adjustsFontSizeToFit as new prop for Button

**Is your feature request related to a problem? Please describe.**
On some devices button text gets truncated due to `numberOfLines={1}` being applied to the `Text` label.

**Describe the solution you'd like**
`adjustsFontSizeToFit` exists and provides an easy way to keep the entire label visible.

**Describe alternatives you've considered**
I have attempted to do this myself by passing a `Text` element as a child to the button like so:
```

{text}

```
This unfortunately did not work. Only by editing the `Button` itself did iOS respect the `adjustsFontSizeToFit` prop.
**Additional context**
It looks like there is an existing pull request for this (although it's missing context):
#4125

Start at the Button implementation that renders the Text label, then review the context of pull request #4125. Expose adjustsFontSizeToFit as a Button prop and verify that the label remains visible on iOS when the text would otherwise be truncated.

Written by the indexing model from the issue text.