de-kebab-ify pseudo-classes

[kevinbarabash]

I recently had to use ::-moz-focus-inner to fix an issue. It would be nice if ::MozFocusInner work so that there's consistency between how normal properties and pseudo-classes work.

[lencioni]

I'm not convinced about that the value is worth the additional code complexity here. For normal properties, being able to convert from camelCase to kebab-case is really useful to make it easier for devs to type out all of those styles (e.g. don't have to add quotes around the keys). Since these styles already require quotes because of the colons, we won't get that benefit. Thoughts?