fix(mssql): upsert query with falsey values (#12453)

[patrickcarnahan]

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Description of change

cherry-pick of #12453

properly determines if a value used in a filter clause for upsert is relevant. currently there is a bug where it treats "falsey" values as not being specified, making it impossible to use something like a default value of 0 in a unique key and then filter by that value.

closes #11902
closes #11684

[codecov]

Codecov Report

Merging #12459 into v6 will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##               v6   #12459   +/-   ##
=======================================
  Coverage   96.44%   96.44%           
=======================================
  Files          95       95           
  Lines        9154     9154           
=======================================
  Hits         8829     8829           
  Misses        325      325           

Impacted Files	Coverage Δ
lib/dialects/mssql/query-generator.js	95.69% <100.00%> (ø)

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[sushantdhiman]

🎉 This PR is included in version 6.3.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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