fix(data-security): data masking failed when using nesting case-when clause

[smallsheeeep]

What type of PR is this?

type-bug
module-data security

What this PR does / why we need it:

When executing following SQL (with nesting case-when), then masking failed due to extract sensitive column failed:

SELECT
  id,
  name,
  CASE
    WHEN birthday < '1990-01-01' THEN 1
    WHEN birthday < '2010-01-01' THEN CASE
      WHEN birthday < '2005-01-01' THEN 21
      WHEN birthday < '2010-01-01' THEN 22
    END
    WHEN birthday < '2020-01-01' THEN 3
    ELSE 4
  END AS decade
FROM
  test_data_masking_1;

The root cause is that the column extractor does not consider syntactic scenarios where case-when is nested within case-when. This PR fix it and add unit test.

By the way, the incorrect file formatting in .editconfig causing indentation configuration to not take effect, incidentally fixed.

Which issue(s) this PR fixes:

Fixes #1391

Special notes for your reviewer:

Self-test passed.

Additional documentation e.g., usage docs, etc.:

[yhilmare]

lgtm