Include MultiLineString output type for greatCircle module

[kronick]

This PR updates the Typescript type definitions and corresponding docs for the greatCircle function to include the possibility of returning a MultiLineString when the input spans the antimeridian. This is described as expected behavior in this issue. Without this fix, Typescript will return an error if you try to test, for example:

const greatCircleGeojson = greatCircle(start, end);
if(greatCircleGeojson?.geometry.type === "MultiLineString") {
 // ... handle this case
}

Typescript complains: This condition will always return 'false' since the types '"LineString" | undefined' and '"MultiLineString"' have no overlap.

[rowanwins]

Looks great, thanks @kronick !

[kronick]

@rowanwins Thanks for the ✅ — will you handle merging this for the next release? Is there anything else I need to do?

[regileeso]

I'd love to see these changes in a new release as soon as possible 👍