[Messenger] Add mobile props to choose between web link or app link

[GautierT]

Hi.

https://www.facebook.com/dialog/send doesn't work on mobile and fb-messenger://share doesn't work on desktop.
So i added a new props mobile.

• When true it will use fb-messenger://share
• When false it will use https://www.facebook.com/dialog/send

<FacebookMessengerShareButton
        url={url}
        mobile={isMobile}
        appId='************'
        className='share_button'
      >
        <FacebookMessengerIcon size={32} round />
</FacebookMessengerShareButton>

[sirpy]

@nygardk can we merge this?
also @GautierT @nygardk can we add this to facebook on android mobile? this will open the native facebook app. but it doesntt work on iOS:(
fb://faceweb/f?href=https://m.facebook.com/sharer.php?u=<url>