Enable property functions for line-width

[lbud]

Supersedes #9214 — this version uses no special case code generation. Instead it evaluates LineFloorwidth with a bool useIntegerZoom = true parameter, which is passed on to its function members, although I'm not sure if this might be sketchy (particularly in the spot where it copies parameters.useIntegerZoom to a copy of a const function argument here) … ?

[lbud]

This is passing render tests but fails to compile on several builds, e.g. https://circleci.com/gh/mapbox/mapbox-gl-native/4747 😕

[jfirebaugh]

Does it work if you add an explicit constructor?

    evaluated = RenderLinePaintProperties::PossiblyEvaluated(
        unevaluated.evaluate(parameters).concat(extra.evaluate(dashArrayParams)));

[lbud]

A few tiny platform-specific docs changes snuck in as collateral damage ( here and here ) but they look like harmless docs improvements that weren't generated in a prior commit.