fix(sqla): Normalize prequery result type

[john-bodley]

SUMMARY

This PR fixes a regression introduced in #16795 as not all temporal columns are of type TIMESTAMP. The solution (as outlined in #16795 (comment)) uses the SQLA connector to convert the date time appropriately.

TESTING INSTRUCTIONS

Added unit tests and tested locally.

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #17312 (734de96) into master (79ed0ae) will increase coverage by 0.00%.
The diff coverage is 91.66%.

@@           Coverage Diff           @@
##           master   #17312   +/-   ##
=======================================
  Coverage   77.09%   77.09%           
=======================================
  Files        1037     1037           
  Lines       55646    55650    +4     
  Branches     7607     7607           
=======================================
+ Hits        42900    42905    +5     
+ Misses      12496    12495    -1     
  Partials      250      250           

Flag	Coverage Δ
hive	81.56% <91.66%> (+0.01%)	⬆️
mysql	81.98% <91.66%> (+0.01%)	⬆️
postgres	81.99% <91.66%> (+0.01%)	⬆️
presto	81.86% <91.66%> (+<0.01%)	⬆️
python	82.49% <91.66%> (+<0.01%)	⬆️
sqlite	81.67% <91.66%> (+0.01%)	⬆️

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Impacted Files	Coverage Δ
superset/utils/core.py	90.09% <ø> (-0.05%)	⬇️
superset/connectors/sqla/models.py	87.86% <91.66%> (+0.46%)	⬆️
superset/db_engine_specs/presto.py	89.95% <0.00%> (-0.42%)	⬇️
superset/db_engine_specs/druid.py	86.27% <0.00%> (ø)

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[villebro]

I agree with the functional change of using the native column type as the basis of the conversion, thanks for the improvement. However, AFAIK the walrus operator will break Python 3.7 compatibility, so we should not use it before we remove explicit support for that version from setup.py.

[villebro]

As we still support Python 3.7, I don't think we can start using the walrus operator quite yet

[john-bodley]

@villebro thanks for the review. I've addressed your comments.

[villebro]

LGTM 👍