Preferred image alignment in UIBlock2D

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Reason

When the scale mode of an image is set to Fit or Envelope, Nova currently aligns them to the center by default:

This makes certain UIs more complex to build, for example, the grading icon as highlighted:

When swapped with another image with a smaller width becomes:

Where ideally, it should be aligned to the left edge:

Proposal

When either Fit or Envelope is selected as the scale mode, show a dropdown to pick the preferred image alignment to fit it to the preferred edge (UDLR).