[TIMOB-8119] MobileWeb: Splash screen shows artifacts when changing orientation or resizing

The splash screen needs to be position:fixed, top:0, left:0, right:0, and bottom:0 during launch. After launch, if the browser is resized or orientation is changed, you can see the splash screen while the layout system waits to render the screen again. We either need to break parity with ios and android and hide the splash screen once a window is opened and then show it again when all windows are closed -or- we need to reset the splash screen's right and bottom and override the width and height with the browser size during the layout function so that they are synced.