feat(generator): connection respects per call policies

[dbolduc]

Fixes #8002

First commit has the logic changes in generator/
Second commit has the changes to the golden files
Third commit has the changes to generated libraries in google/cloud/...

I decided to use if blocks instead of predicates, per this discussion.

We have the following types of calls:

1. Sync Loops - (R, B, I)
2. LRO Polling Loops - (R, B, I, P)
3. Paginated (StreamRange) - (R, B, I)
4. Streaming Reads (StreamRange) - (R, B)
5. Async Loop - (R, B, I)

Letters in parentheses are the policies used in such a call.
R = Retry, B = Backoff, I = Idempotency, P = Polling.

The bold letters are the ones I actually tested for. I did not feel like writing any other tests. I would begrudgingly add more tests, if asked nicely.

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Codecov Report

Merging #8013 (bbc35f8) into main (1927dd7) will decrease coverage by 0.00%.
The diff coverage is 92.77%.

@@            Coverage Diff             @@
##             main    #8013      +/-   ##
==========================================
- Coverage   95.09%   95.09%   -0.01%     
==========================================
  Files        1307     1308       +1     
  Lines      117472   117569      +97     
==========================================
+ Hits       111715   111805      +90     
- Misses       5757     5764       +7     

Impacted Files	Coverage Δ
...ion_tests/golden/golden_kitchen_sink_connection.cc	73.68% <83.87%> (+0.80%)	⬆️
...or/integration_tests/golden/tests/plumbing_test.cc	93.33% <93.33%> (ø)
...tion_tests/golden/golden_thing_admin_connection.cc	77.87% <95.65%> (+1.42%)	⬆️
generator/internal/connection_generator.cc	100.00% <100.00%> (ø)
...cloud/pubsub/internal/subscription_session_test.cc	97.75% <0.00%> (-0.25%)	⬇️
google/cloud/pubsub/samples/samples.cc	92.02% <0.00%> (-0.08%)	⬇️
...integration_tests/schema_admin_integration_test.cc	100.00% <0.00%> (+1.08%)	⬆️
google/cloud/bigtable/internal/common_client.cc	97.14% <0.00%> (+1.42%)	⬆️

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[coryan]

There are a couple of PRs in flight that you may need to coordinate with.

[coryan]

Consider .Times(AtLeast(1)).WillRepeatedly(Return(false)); ?

[dbolduc]

sure

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