feat: add annotation schema tab to annotation panel and editable properties for annotations

[seankmartin]

Readonly datasources get a readonly view of the schema. Editable datasources (e.g. local annotation layers) get an editable version of the schema to add properties to. Editable datasources can also modify properties of annotations from the selection panel.

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[seankmartin]

@chrisj sorry perhaps I used the wrong email? I think the CLA passed with that email before, so apologies there if I have the wrong one.

[stuarteberg]

This looks very cool! I'm excited to try it out.

One thing I've always wished for (for local annotations) is the ability to edit the annotation position itself. Is that possible with this PR?

For box and (especially) ellipsoid annotations, I find it tricky to manipulate the extents exactly how I want using the UI alone. The ability to fine-tune the position with my keyboard would be nice.

One other feature (probably out of scope for this PR) would be to optionally change the annotation type: For lines and boxes, the points remain the same. Transforming to/from ellipsoids requires a trivial calculation.

[seankmartin]

Thanks for the suggestions! I opened the first as an issue with some ideas for now

[fcollman]

@seankmartin I think you need to rebase to get the mac tests to pass.. @chrisj has got the CLA agreement fixed.