SONARPY-282: Rule 1940: Boolean checks should not be inverted (#1090)

* SONARPY-282: Rule 1940: Boolean checks should not be inverted

* Indent the switch function and make an if condition easier to read

* Add 'in' and 'is' rules and simplify

* Fix coverage in switch and add tests

* Add missing expected-file

* More precise tests, descriptions and more appropriate function name

* Improve test

Author: marco-bearzi-sonarsource