Fix legacy `setPenHueToNumber` and `changePenHueBy`
Fix legacy `setPenHueToNumber` and `changePenHueBy`

These two blocks were not doing the same shade-oriented math as
`setPenShadeToNumber`: effectively these blocks were using the new color
model instead of Scratch 2.0's hue-shade model. This change pulls the
hue-shade color update logic into a separate function, now called by all
the legacy pen blocks.

LLK/scratch-vm,LLK/scratch-vm,LLK/scratch-vm