Rework image metadata generation and asset export process

Currently it's two different actions triggered in different export steps, they could fail or successed independently from each other. It leads to us being partially unable to develop good fallback options.

Specifically targeted to fix the problem with exports of invisible items into SVG format - Figma fails to generate an SVG asset of an invisible node. Node can be invisible due to layer visibility and opacity, lack of fill and stroke properties, poor or incomplete vector path, items incorrectly generated from other tools or plugins and other unknown issues.