Support `fontSize` and `lineHeight` for `strong` and `em` styles

[simeonbakalov]

Description

Currently strong and em styles only support inline font styling such as fontFamily, fontStyle, and color.

The final fontSize and lineHeight are inherited from the surrounding block style, for example paragraph, list, or heading styles.

This makes it impossible to style emphasized or strong text with a different size from its surrounding paragraph.

It would be great if more styles are supported for strong and em - fontWeight ("number"), fontSize, lineHeigth etc...

Current API

interface StrongStyle {
  fontFamily?: string
  fontWeight?: "bold" | "normal"
  color?: string
}

interface EmphasisStyle {
  fontFamily?: string
  fontStyle?: "italic" | "normal"
  color?: string
}