Figma Bridge: Export line height properties

The highlighted setting above currently has no effect on the generated QML.

Instead, it should produce something like this:

lineHeight: 32
lineHeightMode: Text.FixedHeight

Note: Simply adding this QML code currently won't produce the expected results however, because Qt Quick Text treats line height differently from CSS/Figma (see QTBUG-108468). We either need QTBUG-108468 to be implemented first, or some workaround to map Figma coordinates to Qt coordinates.