fix(model destroy): Return 0 when options is truncate.

[JuarezLustosa]

Pull Request check-list

• Does npm run test or npm run test-DIALECT pass with this change (including linting)?
• Does the description below contain a link to an existing issue (Closes #[issue]) or a description of the issue you are solving?
• Have you added new tests to prevent regressions?
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Description of change

This close #12164.

I was debugging and realize, the SSCE examples is passing truncate as an option. Therefore truncate on the database does not show affected rows so we can't return the value, thus I found the Postgres NaN in these cases.

• I changed the doc adding info about it when use truncate will no show rows affected only on Sqlite do this.
• Fixed Postgres rowCount when queryResult.rowCount isn't returning
• Fixed MSsql when data is empty return 0 on isBulkDeleteQuery

[codecov]

Codecov Report

Merging #12281 into master will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #12281      +/-   ##
==========================================
+ Coverage   96.33%   96.40%   +0.06%     
==========================================
  Files          95       95              
  Lines        9118     9116       -2     
==========================================
+ Hits         8784     8788       +4     
+ Misses        334      328       -6     

Impacted Files	Coverage Δ
lib/dialects/postgres/query.js	97.83% <ø> (ø)
lib/dialects/mssql/query.js	94.53% <100.00%> (-1.12%)	⬇️
lib/dialects/sqlite/query-generator.js	96.50% <0.00%> (-0.11%)	⬇️
lib/dialects/mysql/query-generator.js	97.56% <0.00%> (-0.06%)	⬇️
lib/dialects/postgres/query-interface.js	98.92% <0.00%> (-0.02%)	⬇️
lib/sequelize.js	95.81% <0.00%> (ø)
lib/transaction.js	100.00% <0.00%> (ø)
lib/associations/helpers.js	100.00% <0.00%> (ø)
lib/dialects/sqlite/query.js	98.18% <0.00%> (ø)
... and 15 more

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