Expose adjustsFontSizeToFit as new prop for Button

[hmhobbs]

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:

<Button onPress={onPressEvent}>
    <Text numberOfLines={1} adjustsFontSizeToFit>
        {text}
    </Text>
</Button>

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