Return color string values in the [0-255] range

[LukasPaczos]

Closes #14130.

Fixes the color string round tripping which makes all the places where the string is used compliant with the rgba color option from the spec. All other color string types will be converted to rgba when being fetched back from the core and we don't have a good mechanism in place to fight that.

String alpha value will be rounded to 2 decimal points.

[LukasPaczos]

String alpha value will be rounded to 2 decimal points.

This is done in 1907c05.

@kkaefer @1ec5 above is to improve color values round-tripping, any issues you're seeing in the approach? Or is there a way to work around CSSColorParser#parse changing the decimal output?

[1ec5]

above is to improve color values round-tripping, any issues you're seeing in the approach? Or is there a way to work around CSSColorParser#parse changing the decimal output?

NSColor on macOS and UIColor on iOS represent all components, including the alpha component, with a double-precision property, whereas the components are all floats in mbgl. Does it make sense to increase the precision, or should we just live with the lack of round-tripping on Apple platforms?

mapbox-gl-native/include/mbgl/util/color.hpp

Lines 27 to 30 in 24361fe

	float r = 0.0f;
	float g = 0.0f;
	float b = 0.0f;
	float a = 0.0f;

/cc @fabian-guerra @julianrex

[LukasPaczos]

Any other thoughts here? Can we get this into release-mojito or does it require further discussion?