Take slur skylines from stencil
The code to build slur skylines predates the ability to build skylines from stencils directly. Use this ability, which removes code duplication. As a bonus, this means that the slur's thickness will factor into its skylines. This makes for plenty of good-natured differences in regression tests, where a slight bit of padding is added in vertical spacing that was previously too tight.
Edited by Jean Abou Samra