refactor: sql_json view endpoint: extract methods

[ofekisr]

The sql_json view code in superset core view without any "clean code" standard and it does not adopt any software development principle.
This is the ninth PR in the sequence of future PRs (previous PR) try to solve it by refactoring the code.
The PR focus of extract code to methods and arrange the code by flow ordering

[amitmiran137]

LGTM

[codecov]

Codecov Report

Merging #16675 (57f808a) into master (bb014b5) will decrease coverage by 0.06%.
The diff coverage is 74.56%.

❗ Current head 57f808a differs from pull request most recent head d6ebd4b. Consider uploading reports for the commit d6ebd4b to get more accurate results

@@            Coverage Diff             @@
##           master   #16675      +/-   ##
==========================================
- Coverage   76.90%   76.84%   -0.07%     
==========================================
  Files        1005     1005              
  Lines       54005    54019      +14     
  Branches     7337     7337              
==========================================
- Hits        41534    41509      -25     
- Misses      12231    12270      +39     
  Partials      240      240              

Flag	Coverage Δ
hive	81.24% <74.56%> (+<0.01%)	⬆️
mysql	81.59% <72.11%> (-0.03%)	⬇️
postgres	81.69% <74.56%> (+<0.01%)	⬆️
presto	?
python	82.05% <74.56%> (-0.14%)	⬇️
sqlite	81.26% <72.11%> (-0.07%)	⬇️

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Impacted Files	Coverage Δ
superset/views/core.py	76.20% <73.87%> (+0.20%)	⬆️
superset/tasks/scheduler.py	68.88% <100.00%> (+1.44%)	⬆️
superset/db_engine_specs/presto.py	84.51% <0.00%> (-5.44%)	⬇️
superset/connectors/sqla/models.py	88.28% <0.00%> (-1.43%)	⬇️
superset/models/core.py	89.14% <0.00%> (-0.26%)	⬇️

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