Allow percentages for line height

[Matty_Vazquez]

This is needed! Also seems to be similar to these threads about %:

Use percentage for size variables

Hello. I was wondering if it is possible to have percentage values in variables, like setting percentage value for frame widths or shape sizes (etc.) that have variable modes applied to them? Percentage values could respond better to content that varies within a frame or frames within frames.

Use percentages for heights, widths, margins, gutters in auto layout

This makes it easier to use components in designs for different screen sizes. And then you don’t have to calculate every time what 40% or 60% of the width is. This also makes it easier to design scalable applications that grow with the width of the screen.