feat: custom emoji text style

[Bad-Science]

This small PR adds a text style param for the single emoji component.

This change is to the end of supporting custom fonts. For example, here is RN Emoji Keyboard with NotoEmoji:

...
<EmojiKeyboard
  styles={{
    emoji: {
      text: {
        fontFamily: "NotoEmoji-Bold",
        fontSize: 32,
        color: "#10b98f"
      }
    }
  }}
...
>

[Bad-Science]

Any interest in including this? Happy to make changes if needed