Finer man_made=pier width

[meased]

Fixes #2652

• Lowers the stroke width of man_made=pier
• Adds square line-cap to remove rendering artifacts
• Does not effect piers mapped as an area

From the discussion in #2652, there was some disagreement on whether piers should represent real world geometries or abstract lines. My opinion is that it doesn't matter which camp you're in, piers are currently much wider in the map than they are in the real world, and as an abstract line, they are still too wide (they are wider than residential roads at zooms 12, 13 and 14).

At this sample area.

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Notice the gaps in the line rendering.
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[HolgerJeromin]

All roads have round as cap.

[meased]

Round would look best when two sections join at a non-right angle, but I didn't know how people would feel about round pier ends.

[HolgerJeromin]

Yes, the pier ending. You are right

[imagico]

For better understanding - this is the line width on the ground (in meters) the proposed change would result in for the different zoom levels.

zoom	line-width	ground width (Equator)	ground width (60°)
12	0.5	19	9.5
13	1	19	9.5
14	1	9.5	4.8
15	2	9.5	4.8
16	2	4.8	2.4
17	4	4.8	2.4
18	4	2.4	1.2

[kocio-pl]

I like this proposition.

[kocio-pl]

Regarding width table - I think they are so thin after the change, that it's just a hint that they are here. Which is good, because they are too visible now. And if you want real size and shape, you should map them as area - which is preferred as more accurate.