feat(storage): equality for Native IAM types

[dbolduc]

Part of the work for #2310

The types are:

• storage::NativeExpression
• storage::NativeIamBinding
• storage::NativeIamPolicy

And I was too lazy to do this internal type in a separate PR:

• storage::internal::PatchBuilder

---

This change is 

[google-cloud-cpp-bot]

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For commit: 65f47239128e2a7e06cab02880e2b741ef5b604e

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[codecov]

Codecov Report

Merging #9649 (0af2b5e) into main (a508bb6) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #9649   +/-   ##
=======================================
  Coverage   94.35%   94.36%           
=======================================
  Files        1493     1493           
  Lines      138786   138839   +53     
=======================================
+ Hits       130956   131012   +56     
+ Misses       7830     7827    -3     

Impacted Files	Coverage Δ
google/cloud/storage/iam_policy.cc	98.92% <100.00%> (+1.19%)	⬆️
google/cloud/storage/internal/patch_builder.cc	83.60% <100.00%> (+3.09%)	⬆️
...oogle/cloud/storage/internal/patch_builder_test.cc	92.24% <100.00%> (+0.44%)	⬆️
google/cloud/storage/storage_iam_policy_test.cc	100.00% <100.00%> (ø)
...bigtable/examples/bigtable_hello_instance_admin.cc	81.00% <0.00%> (-2.00%)	⬇️
...ud/spanner/integration_tests/client_stress_test.cc	84.21% <0.00%> (-0.66%)	⬇️
google/cloud/pubsub/subscriber_connection_test.cc	97.75% <0.00%> (-0.57%)	⬇️
...e/cloud/pubsublite/internal/alarm_registry_impl.cc	100.00% <0.00%> (+2.94%)	⬆️

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[google-cloud-cpp-bot]

Google Cloud Build Logs
For commit: 0af2b5e6cd39017e05de5501505a1a68c07eff1d

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• Cloud Build Console (requires auth)
• Kokoro Logs (requires auth)

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