proper applicability for obfuscated_if_else

[lapla-cogito]

fix #14034

The currect implementation of obfuscated_if_else sometimes makes incorrect suggestions when the original code have side effects (see the example in the above issue). I think this can be fixed by changing the applicability depending on whether it can have side effects or not.

changelog: [obfuscated_if_else]: change applicability when the original code can have side effects

[rustbot]

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[lapla-cogito]

Rebased to resolve conflicts.