Render unpaved roads differently

[pastk]

Especially for vehicle navigation mode its important to visually hint the driver that a road is unpaved / bad surface quality.

There was an attempt to do it already, in data/styles/vehicle/include/Roads.mapcss there is:

line|z14[psurface=unpaved_good],
line|z14[psurface=unpaved_bad]
{width: 1.4;dashes: 2,1.35;}

The idea was to draw a dashed line on top of the main road line if a feature has psurface-unpaved_good/bad type (its a specially processed type that combines smoothness and surface tags).

ATM its effectively disabled. To enable increase psurface-unpaved_good/bad line priorities to be higher than highways' and change their color to something more visible on white.

It needs some experimenting with line's color, thickness and dash pattern to be usable and look good when applied to different road types. I think in some countries (e.g. Mongolia) even major primary/trunk roads (colored orange) could be unpaved.

[RedAuburn]

I really like the faint grain that Carto recently added (link to PR), not sure how possible it would be to implement though

[pastk]

There was an attempt to do it already, in data/styles/vehicle/include/Roads.mapcss there is:

line|z14[psurface=unpaved_good],
line|z14[psurface=unpaved_bad]
{width: 1.4;dashes: 2,1.35;}

In the current form it lead to bugs, see

• Fix [footway][sac_scale] color and [unpaved_*] rendered as footways #6946
  I.e. presence of a psurface-unpaved_bad type made a highway-path visible on low zooms and rendered as a footway.

So we need a better approach.

[pastk]

Probably the same mechanism should be used

• Display highways with access=no/private grayed out #1454