turf-tessellate: Pass original coordinate elevations through the tessellate function.

[prozvora]

Summary of Changes

Pad elevation coordinate member with undefined for passing to earcut.
Strip off undefined elevations before returning result from tessellate.
Add test case for constant elevation in all coordinates.
Add test case for variable elevation in some coordinates.

Note

This is a non-breaking change.

Resolves

• The @turf/tesselate function fails to properly process GeoJSON Polygon data that includes elevation. #2672

Test Output

Tessellate

# tesselate
ok 1 Polygon returns a FeatureCollection
ok 2 contains at least 1 triangle
ok 3 triangle is valid
ok 4 MultiPolygon returns a FeatureCollection
ok 5 contains at least 1 triangle
ok 6 triangle is valid
ok 7 should throw
ok 8 should throw
ok 9 Polygon returns a FeatureCollection
ok 10 contains at least 1 triangle
ok 11 triangle is valid
ok 12 triangle coordinates contain elevation
ok 13 Polygon returns a FeatureCollection
ok 14 first triangle coordinates contain original elevations
ok 15 second triangle coordinates contain original elevations

1..15
# tests 15
# pass  15

# ok

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