Revalidate stages upon view reload

[brimoor]

Calling reload() now causes view stages to be re-validated, which allows for views to take into account any changes to the underlying dataset that occurred after the view is created.

In general, one can always reconstruct views from scratch, but reload() is now more a more viable option in cases where it is desired to continue using an existing DatasetView instance while a dataset may be changing underneath.

Example use case:

import fiftyone as fo
import fiftyone.zoo as foz

dataset = foz.load_zoo_dataset("quickstart")
view = dataset.select_fields("uniqueness")

dataset.delete_sample_field("uniqueness")

# Immediately raises an error, since `uniqueness` field was deleted
view.reload()
# ValueError: Field 'uniqueness' does not exist

[codecov]

Codecov Report

Patch coverage: 82.87% and project coverage change: +0.07 🎉

Comparison is base (3311694) 61.97% compared to head (80785a4) 62.05%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2890      +/-   ##
===========================================
+ Coverage    61.97%   62.05%   +0.07%     
===========================================
  Files          259      259              
  Lines        43808    43974     +166     
  Branches       350      350              
===========================================
+ Hits         27150    27288     +138     
- Misses       16658    16686      +28     

Flag	Coverage Δ
app	48.60% <35.41%> (-0.03%)	⬇️
python	99.43% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
app/packages/looker/src/overlays/heatmap.ts	16.06% <0.00%> (-0.33%)	⬇️
app/packages/looker/src/overlays/util.ts	25.25% <16.66%> (-1.19%)	⬇️
app/packages/state/src/recoil/selectors.ts	43.92% <27.27%> (-0.85%)	⬇️
app/packages/looker/src/worker/index.ts	100.00% <100.00%> (ø)
tests/unittests/aggregation_tests.py	99.65% <100.00%> (+0.01%)	⬆️
tests/unittests/dataset_tests.py	99.84% <100.00%> (+<0.01%)	⬆️
tests/unittests/similarity_tests.py	97.95% <100.00%> (+0.52%)	⬆️
tests/unittests/view_tests.py	99.86% <100.00%> (+<0.01%)	⬆️

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