* Atom/qingtao/lyn 3436 (#558)
* LYN-3436 AutomatedTesting.GameLauncher crashes at launch if assets are not all processed
Change RPISystem so that the application would exit if the RPI system couldn't load critical assets.
Added code to avoid the GetLayout crash when layout for each platforms were not ready.
Added LoadCriticalAsset function to force compile and load critical assets.
Added default value to viewport size for ViewportContext.
* Change RPISystem asset initialization order so it returns earlier when those critical assets are not ready
moudgils
Vicky
alexpete