Make async connect work on MacOS: it is necessary top call WaitLatchOrSocket before PQconnectPoll

[knizhnik]

Problem

While investigating problem with test_subscriber_restart flukyness, I found out that this test is not passed at all for PG 14/15 at MacOS (while working for PG16).

Summary of changes

Rewrite async connect state machine exactly in the same way as in Vanilla: call WaitLatchOrSocket with WL_SOCKETR_WRTEABLE before calling PQconnectPoll.

Please notice that most likely it will not fix flukyness of test_subscriber_restart.

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

3276 tests run: 3155 passed, 0 failed, 121 skipped (full report)

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Flaky tests (5)

Postgres 16

• test_sharding_split_compaction[compact-shard-ancestors-localonly]: debug
• test_change_pageserver: debug

Postgres 15

• test_change_pageserver: debug
• test_cancellations: debug

Postgres 14

• test_scrubber_physical_gc_ancestors[2]: debug

Code coverage* (full report)

• functions: 32.6% (7005 of 21497 functions)
• lines: 50.0% (55259 of 110586 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
98743ea at 2024-07-24T05:50:30.413Z :recycle:}