GeoDataset: add support for slicing

[adamjstewart]

This PR adds support for GeoDataset slicing, and is part of ongoing work to add time series support to TorchGeo: #2382.

Before

ds[BoundingBox(xmin, xmax, ymin, ymax, tmin, tmax)]

After

ds[xmin:xmax, ymin:ymax]
ds[:, :, tmin:tmax]
ds[xmin:xmax:xres, ymin:ymax:yres, tmin:tmax:tres]

Progress

• [x] Dataset Base Classes
  • [x] GeoDataset
  • [x] RasterDataset
  • [x] VectorDataset
  • [x] IntersectionDataset
  • [x] UnionDataset
• [x] Custom Datasets
  • [x] AgriFieldNet
  • [x] Chesapeake CVPR
  • [x] EDDMapS
  • [x] EnviroAtlas
  • [x] GBIF
  • [x] GlobBiomass
  • [x] iNaturalist
  • [x] LandCover.ai
  • [x] Open Buildings
  • [x] South Africa Crop Type
• [x] Samplers
  • [x] GeoSampler
  • [x] RandomGeoSampler
  • [x] GridGeoSampler
  • [x] PreChippedGeoSampler
  • [x] BatchGeoSampler
  • [x] RandomBatchGeoSampler
• [x] Documentation
• [x] Testing

Backwards-Incompatible Changes

• GeoDatasets are now indexed by GeoSlice, not BoundingBox
• GeoDataset.bounds now returns a GeoSlice, not BoundingBox
• Returned sample bounds are now a GeoSlice, not BoundingBox
• get_random_bounding_box now takes a tuple as input and returns a tuple
• tile_to_chips now takes a tuple as input