Rename allowBooleanNegation to isBooleanFlag

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (0654af0) 98.77% compared to head (d38319c) 98.77%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #149 +/- ## ======================================= Coverage 98.77% 98.77% ======================================= Files 27 27 Lines 1789 1793 +4 ======================================= + Hits 1767 1771 +4 Misses 22 22 ```

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[andrey-zherikov]

Fixed :-D