CHTML doesn't scale bounding box for content in unknown fonts in script sizes.

When CHTML needs to measure content that is in a non-MathJax font (e.g., unicode characters not in its fonts, or when mtextInheritFont is used, or when an explicit font is specified in a style attribute), it fails to account for the scaling for script and script-script sizes. See this StackOverflow post for an example.

The unknownText() function needs to be passed the relative scaling factor from the element's BBox structure and compensate for that.