GUI image 'object-position'

Hi,

I’m playing a bit with the GUI system. I’m generally a bit proponent of Images’ aspect-fill or object-fit: contain or babylon’s STRETCH_UNIFORM. Babylon lacks a bit of a feature for this to work in all cases though. I would really like to see something similar to the css object-position. Currently the STRETCH_UNIFORM is only useful for centered content.
We for example want an image in the bottom right corner with some margins, but also uniformly scaled. Currently that’s not really doable with STRETCH_UNIFORM.

I’d like a property so that we have control over its alignment when STRETCH_UNIFORM is used. The existing transformCenterY/transformCenterX or verticalAlignment/horizontalAlignment properties could also be used for this, but there are probably also cases where you want to have different values in each case.

cc @carolhmj