feat(image-cropper-web): allow custom aspect ratio width/height as expressions

[hunter-koppen]

Convert the customAspectWidth/customAspectHeight properties from static integers to Integer-returning expressions so mendix developers can bind an attribute (or any expression) to the ratio sides instead of a fixed value.

The store now reads each DynamicValue via ValueStatus.Available guard, resolveAspectRatio tolerates undefined, and the editor preview parses the expression text (numeric literals only) with a free-aspect fallback.

[leonardomendix]

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