[ConstraintSystem] Use `findSelectedOverloadFor` in `isArgumentGeneri…

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…cFunction`

Fixes a crash when existing logic cannot properly determine whether argument is resolved or not.

Instead of ad-hoc code that checks ResolvedOverloads directly, let's use a method that would reach of a callee locator to determine whether argument is a reference to a generic function or not.

Resolves: rdar://137825558

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@swift-ci please test

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@swift-ci please test Windows platform