Read and skip validity buffer of UnionType Array for V4 ipc message

[viirya]

Which issue does this PR close?

Closes #1788.

Rationale for this change

What changes are included in this PR?

Are there any user-facing changes?

[codecov-commenter]

Codecov Report

Merging #1789 (ea61242) into master (940b5b5) will decrease coverage by 0.00%.
The diff coverage is 78.94%.

@@            Coverage Diff             @@
##           master    #1789      +/-   ##
==========================================
- Coverage   83.39%   83.39%   -0.01%     
==========================================
  Files         198      198              
  Lines       56171    56205      +34     
==========================================
+ Hits        46846    46872      +26     
- Misses       9325     9333       +8     

Impacted Files	Coverage Δ
arrow-flight/src/utils.rs	0.00% <0.00%> (ø)
...ng/src/flight_client_scenarios/integration_test.rs	0.00% <0.00%> (ø)
...ng/src/flight_server_scenarios/integration_test.rs	0.00% <0.00%> (ø)
arrow/src/ipc/reader.rs	90.73% <86.66%> (-0.11%)	⬇️
arrow/src/ipc/writer.rs	80.93% <100.00%> (+0.55%)	⬆️
parquet/src/encodings/encoding.rs	93.46% <0.00%> (-0.20%)	⬇️
parquet_derive/src/parquet_field.rs	65.98% <0.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 940b5b5...ea61242. Read the comment docs.

[nevi-me]

LGTM. Do we need to do anything for write support?

[viirya]

Thanks @nevi-me

Yes, if specifying metadata_version as V4, the ipc writer also need to write validity buffer for UnionType Array. Currently it doesn't, although it doesn't affect the interop test.

I will create another PR after this for writer change and test.

[alamb]

👍