[editable-layers] Update to turf 7 and use geojson types

[timnyborg]

This is an attempt at updating editable-layers to rely on turf.js@7 to remove the type carnage that came from competing geojson, turf.js, and nebula.gl type definitions.

• Mostly changes to replace the custom nebula Feature and FeatureCollection types with geojson's, narrowing to exclude GeometryCollection (which is unsupported)
• Updates a few calls where turf.js functions now require FeatureCollection inputs (intersect, difference, etc.) or return a Feature (centroid)
• Updates a couple values in tests, due to an upstream fix in @turf/area
• Drops a lot of unneeded ts-expect-errors. Leaves a few type assertions in place to avoid additional functional changes, but the type safety is much improved
• Updates "mode handlers", even though they seem to be long dead. Should they just be dropped from the package?
• Drops code from long, long dead lib folder, and an unused curve-utils file, rather than trying to update turf usages there.

Assuming the PR is otherwise acceptable, I'm unsure what other work might need to be done. Other modules in the repo specify turf 6.5, so we might want to update them as well (examples, examples-wip, react, website)

Addresses #202

[timnyborg]

Probably want to drop this export, and have all files import directly from geojson instead - this was a quick way to make the switch.

[charlieforward9]

@timnyborg id like to see this land before integrating the editable-layers into my repo. What additional work is required here?

[timnyborg]

@charlieforward9 as far as I'm concerned, none, as this is passing the test suite for me. It's really a question for the repo owners, though.

Note that you can use this library with turf@7, which is almost entirely backwards-compatible with v6, just with the odd type assertion around Feature, etc.

[charlieforward9]

That's fantastic to hear. In this case, let's see if @ibgreen can review and land it! I'm eager to get editable layers as up to date and functional as possible as I have 2 projects depending on it