Enable property functions for line-width

[lbud]

Counterpart of mapbox/mapbox-gl-js#4773.

To accomplish the same special casing here this PR

• adds a line-floorwidth property at runtime in generate-style-code.js when it encounters line-width, with a skip: true property used by other ejs files to selectively generate property classes
• the generated LineLayer::setLineWidth method sets LineFloorwidth as the same time as it sets LineWidth, and immediately marks that property to useIntegerZoom():
• DataDrivenPropertyValue::useIntegerZoom() sets a bool useIntegerZoom on function values, which are used to determine whether to floor a zoom value in evaluating camera and composite functions

One thing I wasn't sure about was the evaluate() in src/mbgl/renderer/possibly_evaluated_property_value.hpp (this TODO) — in manually testing this with multiple combinations of constant/camera/source/composite functions, I never hit this breakpoint — how is this used, and is it also somewhere we should conditionally evaluate using integer zooms?

[lbud]

Er — investigating a few render tests ⚒ ✅

[lbud]

Superseded by #9250.