convert 062_defer_state_tests

[jtcohen6]

resolves #6613
resolves #6617

Backport to 1.4.latest after merging (see #6617 (comment))

Description

• Converted to pytest framework
• Replace direct file reads/writes with common test utilities (write_file, rm_file). I was a bit inconsistent in terms of what I defined in + imported from fixtures.py, and what I just kept as strings defined inline.
• These are complex & intricate test sequences. I did some light refactoring in places where tests had been over-aggressively duplicated over time, but I kept most of them.
• As part of that refactoring work, I found a bug in the implementation of --favor-state that's currently included in v1.4.0-rc1 (feature/favor-state-node #5859). I'll open a separate issue + PR to include that commit. We should backport this PR to 1.4.latest, and include the fix for v1.4.0-rc2.
• I do not believe this test needs to be run on any other adapters; it's completely core functionality. As such, I added it to tests/functional rather than tests/adapter, and I'll open follow-up PRs in adapter repos to remove this test entirely.

Adapter PRs

• Rm defer_state_test dbt-redshift#268
• Rm defer_state_test dbt-snowflake#397
• Rm defer_state_test dbt-bigquery#468

Checklist

• I have read the contributing guide and understand what's expected of me
• I have signed the CLA
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• I have opened an issue to add/update docs, or docs changes are not required/relevant for this PR
• I have run changie new to create a changelog entry

[McKnight-42]

Favor state isn't a config i've heard of so will look into that a bit more, but the tests themselves all make sense and I don't see any logical issues

[jtcohen6]

I forgot I included a commit (fa9d2a0) that reverted the fix (083d310), just to prove that the converted test really does catch the bug + prove the fix!

Reverting the revert now...