fix ring orientation for ST_AsMVTGeom and add orientation tests

[hafenkran]

Switched ST_AsMVTGeom to orient polygons the right way after the Y‑flip, so exterior rings are CW and holes are CCW in tile coords (as per the MVT spec). Added tests covering a polygon, a polygon with a hole, and a multipolygon to lock this in.

Example:

D SELECT ST_AsText(
      ST_AsMVTGeom(
          ST_GeomFromText('POLYGON((0 0, 1 0, 1 1, 0 1, 0 0))'),
          ST_Extent(ST_GeomFromText('POLYGON((0 0, 2 0, 2 2, 0 2, 0 0))')),
          4096
      )
  );
┌──────────────────────────────────────────────────────────────────────────────────────────┐
│ st_astext(st_asmvtgeom(st_geomfromtext('POLYGON((0 0, 1 0, 1 1, 0 1, 0 0))'), st_exten…  │
│                                         varchar                                          │
├──────────────────────────────────────────────────────────────────────────────────────────┤
│ POLYGON ((2048 4096, 0 4096, 0 2048, 2048 2048, 2048 4096))                              │
└──────────────────────────────────────────────────────────────────────────────────────────┘

Closes #731

[Maxxen]

Thanks for the PR! LGTM!

[Maxxen]

(don't worry about the windows failure, I will have to deal with it myself soon anyway)