[BEAM-1251] Use Python 3 semantics in Cython-compiled modules.

[tvalentyn]

Please add a meaningful description for your change here

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Post-Commit Tests Status (on master branch)

Lang	SDK	Dataflow	Flink	Samza	Spark	Twister2
Go		---		---		---
Java
Python				---		---
XLang				---		---

Pre-Commit Tests Status (on master branch)

---	Java	Python	Go	Website	Whitespace	Typescript
Non-portable
Portable	---		---	---	---	---

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GitHub Actions Tests Status (on master branch)

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[tvalentyn]

Run Dataflow Python 3.7 PostCommit

[tvalentyn]

Run Python 3.7 PostCommit

[tvalentyn]

Run Python 3.8 PostCommit

[tvalentyn]

Run Python 3.6 PostCommit

[tvalentyn]

Run Python 3.7 PostCommit

[tvalentyn]

Run Dataflow Python ValidatesRunner

[tvalentyn]

Run PYthon Dataflow ValidatesRunner

[codecov]

Codecov Report

Merging #14198 (27f713d) into master (e3367a1) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #14198      +/-   ##
==========================================
- Coverage   83.15%   83.14%   -0.01%     
==========================================
  Files         469      469              
  Lines       58946    58924      -22     
==========================================
- Hits        49016    48995      -21     
+ Misses       9930     9929       -1     

Impacted Files	Coverage Δ
...ks/python/apache_beam/runners/worker/data_plane.py
...s/sdks/python/apache_beam/io/gcp/tests/__init__.py
...y38/build/srcs/sdks/python/apache_beam/io/kafka.py
...beam/runners/interactive/display/pipeline_graph.py
...py38/build/srcs/sdks/python/apache_beam/io/jdbc.py
...ild/srcs/sdks/python/apache_beam/transforms/sql.py
...ython/apache_beam/io/gcp/datastore/v1new/helper.py
...on/apache_beam/runners/dataflow/dataflow_runner.py
...beam/runners/portability/local_job_service_main.py
...am/testing/benchmarks/nexmark/models/field_name.py
... and 928 more

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[tvalentyn]

R: @lazylynx

[lazylynx]

LGTM, thanks @tvalentyn