Add rendering for water slides (attraction=water_slide)

[johsin18]

Expected behavior

Should be rendered as a path (blueish?) and an appropriate icon if mapped as a way.
Should be rendered as just the icon if mapped as a node.
The icon could be a man on a sloping line.

Actual behavior

Not rendered at all.

Links and screenshots illustrating the problem

Tag description:
https://wiki.openstreetmap.org/wiki/Tag:attraction%3Dwater_slide
It "suggests" to make it waterway=stream in addition, to force it being rendered, but is that a valid approach?

Example occurrence:
https://www.openstreetmap.org/#map=19/47.52249/7.56949

[kocio-pl]

I guess it should be rendered the same as a stream, but with the dark blue outline (to show similarity to swimming pool). I would probably not render nodes and icons.

Would you like to try make the code? We lack coders, so it's best to try on your own.

[matthijsmelissen]

I think this is too specific for our general purpose map.

[kocio-pl]

With generic water-like rendering I don't see the problem. It would look like swimming pool extension and won't create problem anywhere else.

[HolgerJeromin]

Our waterpark icon is similar than the suggested icon, isnt it?

[johsin18]

So I will try to come up with a PR. However, it seems that "attraction=*" without "tourism=attraction" is not rendered at all so far, so I also have to change some DB queries.
Into what .mss file should it be inserted? water.mss, amenity_point.mss, or water-features.mss? Or even a new one? I guess I should not integrate it too tightly with waterway=stream, should I?