Change quarry outline to 10% darkened quarry color

[jeisenbe]

Fixes part of #3976

Changes proposed in this pull request:

• Change quarry outline to 10% darkened quarry color rather than gray
• This makes the outline significantly lighter, and clearly different than a barrier

Currently the quarry outline looks similar to a fence or wall on untagged land. This makes it hard to tell if a quarry is surrounded by a wall or fence, or not.

I also tested darken(@quarry, 15%) and darken(@quarry, 20%) but these look too similar to the linear barrier rendering, while the current commit uses darken(@quarry, 10%) and this works well.

This should also make it easier to adapt the style or change the quarry color in the future (though it is always a good idea to adjust the darken percentage if the fill color is lighter or darker than before)

Test rendering with links to the example places:

z16 Slate quarries in Wales - current
https://www.openstreetmap.org/#map=16/53.1243/-4.1475.png

• Note that there is a wall or fence which comes right up to the border between the quarries, but stops there. It appears to be the same color as the quarry outline right now. There are some parts of the quarry outline that also have a wall or fence in that position.

z16 after - 10% darkened @quarry color outline

• Now the quarry outline is clearly lighter than the barrier

z18 current

z18 after

[imagico]

Works fine. The outline is barely visible in a lot of cases with this change but that is not really a problem. Will likely be subject to review for solving #2905.