Add Xenium Explorer GeoJSON import

[wlason]

Problem
Xenium Explorer can export selections as CSV of coordinates or GeoJSON. If the selection area is large, it will refuse to export CSV. CSV is also less compatible with packages like GeoPandas.

Proposed solution
I'd like a spatialdata_io loader similar to spatialdata_io.xenium_explorer_selection. Ideally, I would like it to be able to parse the polygon(s) and store them in the shapes and the cells within the selection in the table. If there are multiple named polygons in the GeoJSON, I would like the names/colours to be preserved. This is biologically very useful, for example in a scenario where multiple tissue sections have been profiles as part of one Xenium 'area'/one output file.

Alternatives
spatialdata_io.xenium_explorer_selection and using CSV of the polygon is the alternative.

I've written a helper script to do this for the dataset I'm working on, perhaps it could be made into a PR with a new function with a little help @LucaMarconato 😊

[LucaMarconato]

Hi @wlason, the solution of the use case you described is a useful one and I'm sure extending xenium_explorer_selection for the geojson would of benefit for multiple users. It would be great if the code you used were made available to other people, either as a PR to spatialdata-io, either hosted somewhere else and with a link to it in this issue.

Regarding opening a PR, I want to disclose that for the next 2 months likely we will have unfortunately limited time for non-core functionalities. We are currently hiring and expanding the team and until then the PR would likely be sitting for a while. When the team is scaled up, we will have more time to go though it.