This will avoid the instantiation of a level of fusion objects and thus should improve performance

…Props

* main:
  TASK: Make BaseUri argument nullable in DummyImageSource constructor
  FIX: Remove preserveAspect
  Replace $allowUpScaling with supportsUpscaling()
  FEATURE: Add quality option
  Empty srcCache on cloning
  TASK: Increase php requirement to 7.4
  BUGFIX: Remove unnecessary named parameter
  FEATURE: Test mixed and invalid descriptors
  BUGFIX: Prevent division by zero
  FEATURE: Implement tests
  FEATURE: Only output existing images and allow upscaling
  Remove superfluous spaces
  Add new line for styleCI
  Add missing end of sentence marker for styleCI
  FEATURE: Runtime cache for `src` method of `AssetImageSource`

# Conflicts:
#	Resources/Private/Fusion/Prototypes/Image.fusion
#	Resources/Private/Fusion/Prototypes/Picture.fusion
#	Resources/Private/Fusion/Prototypes/Source.fusion