[Accessibility] Emoji button couldn't be navigated with tab

Hi, due the emoji button has tabindex=-1 it is skipped by the tab navigation and thus screenreaders couldn’t read it, it would be good to have possibility to configure that or maybe add possibility to provide some custom attributes to override:

<button
          aria-label={native}
          aria-selected={selected || undefined}
          aria-posinset={posinset}
          aria-setsize={grid.setsize}
          data-keyboard={this.state.keyboard}
          title={this.props.previewPosition == 'none' ? emoji.name : undefined}
          type="button"
          class="flex flex-center flex-middle"
          tabindex="-1"
          onClick={() => this.handleEmojiClick({ emoji })}
          onMouseEnter={() => this.handleEmojiOver(pos)}
          onMouseLeave={() => this.handleEmojiOver()}
          style={{
            width: this.props.emojiButtonSize,
            height: this.props.emojiButtonSize,
            fontSize: this.props.emojiSize,
            lineHeight: 0,
          }}
         {...this.props.emojiButtonAttrs}
>

[Charca]

This PR doesn’t make emojis navigable via tab, but it does make them accessible to screen readers https://github.com/missive/emoji-mart/pull/666

[roman-kulakov]

@CSFlorin yes, it could be navigated through arrow keys, but it gives us only a keyboard accessibility but not screenreaders accessibility 😦