feat(isBefore): allow usage of options object

[pixelbucket-dev]

This PR implements steps 1 and 2 of #1874 for isBefore and builds upon #2075.

This PR extracts tests for isBefore into a separate test file ⇾ test/validators/isBefore.test.js (inspired by #1793).

This PR also renames the proposed date option to comparisonDate, because it is more explicit. If verified, it should be implemented in #2075 as well.

Checklist

• PR contains only changes related; no stray files, etc.
• README updated (where applicable)
• Tests written (where applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.96%. Comparing base (f81d857) to head (8b02b7f).
Report is 28 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##            master    #2088      +/-   ##
===========================================
- Coverage   100.00%   99.96%   -0.04%     
===========================================
  Files          110      113       +3     
  Lines         2510     2531      +21     
  Branches       633      643      +10     
===========================================
+ Hits          2510     2530      +20     
- Partials         0        1       +1     

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[WikiRik]

Few remarks, thanks for working on this!

[WikiRik]

Few final comments so that this is consistent with my changes to isAfter and the project in general, but apart from these we should be good I think

[pixelbucket-dev]

I think this should be good to go :).

[WikiRik]

Few remarks to be more in line with how isAfter was done, but those should be my last