Update outliers data check implementation

[angela97lin]

Closes #1745

[codecov]

Codecov Report

Merging #1855 (861da5e) into main (9886fa6) will increase coverage by 0.1%.
The diff coverage is 100.0%.

@@            Coverage Diff            @@
##             main    #1855     +/-   ##
=========================================
+ Coverage   100.0%   100.0%   +0.1%     
=========================================
  Files         260      260             
  Lines       20838    20892     +54     
=========================================
+ Hits        20832    20886     +54     
  Misses          6        6             

Impacted Files	Coverage Δ
evalml/data_checks/data_check.py	100.0% <ø> (ø)
evalml/data_checks/outliers_data_check.py	100.0% <100.0%> (ø)
...ests/data_checks_tests/test_outliers_data_check.py	100.0% <100.0%> (ø)

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[angela97lin]

Private but added some tests anyways for sanity sake / code coverage :)

[freddyaboulton]

@angela97lin Looks great! I have some small comments about cleaning up the apis of the private static methods.

[chukarsten]

Nice, way to knock out this initially poorly defined PR ;). I think we might be able to remove the nan check stuff, but I'll leave that up to you.

[bchen1116]

LGTM! Left one question, but nothing blocking