Support more font weights

[Windisch94]

As for the documentation of the flutter font weight it would be helpful if we can create a mapping between more fonts as Bold and Medium (as for now)

The flutter font specifies the following: (all except thin exist in figma also) /// * [w100]: Thin, the thinnest font weight. (dont exist in figma) /// * [w200]: Extra light. /// * [w300]: Light. /// * [w400]: Normal. The constant [FontWeight.normal] is an alias for this value. /// * [w500]: Medium. /// * [w600]: Semi-bold. /// * [w700]: Bold. The constant [FontWeight.bold] is an alias for this value. /// * [w800]: Extra-bold. /// * [w900]: Black, the thickest font weight.

maybe the figdart plugin can handle these weights also - thanks!