Z-fighting in place=square

[tguen]

TO REPRODUCE THE ISSUE, FOLLOW THESE STEPS:

• open StreetComplete and zoom to this location
• Tilt camera, then pan

RESULT:

The borders of the square and the stairs within it flicker as the camera moves. It looks like it may also be not rendering holes in the multipolygon correctly (the fountains are not visible).

EXPECTED RESULT:

No flickering; border and stairs should be drawn over place=square area

ENVIRONMENT:

StreetComplete 30.0/Android 10/Nokia 6.1
StreetComplete 31.0/Android 11/Google Pixel 4a

OTHER:

Also visible here and here.

Originally reported at streetcomplete/StreetComplete/issues/2612