Add a "Launch Elytra" button to mobile

PC and Console users can instantly jump from the ground and fly away via firework. Doing the same on current touch controls requires jumping once, jumping again, and then holding down the fireworks, a nigh-impossible feat of timing. This not only reduces the value of End Ships for mobile users but could compromise them in combat. My solution is to add this bottom button that only shows when the player is holding non-explosive fireworks AND is wearing an intact Elytra. What it does: My first idea was that it would fully automate the jump > fly > launch 1 fireworks sequence; pressing the button again during the sequence aborts it. A more straightforward concept would be to change the Elytra itself so the first boost from the ground is free, and opens up the wings, but further midair boosts still cost fireworks; 5-10 blocks would give a chance for further flight without risking fatal fall damage or making Riptide obsolete.