fix(spy): fix mockImplementation for function overload and unions

[hi-ogawa]

Description

• closes Type error on mockImplementation with call signature in object type #6155 (broken in v2.0.0)
• closes TypeScript errors when mocking overloaded functions #6182 (broken in v2.0.3)

Previously we had mockImplementation(fn: T) where T extends (...args: any[]) => any, but such T can include arbitrary overload and union types, so it looks like it's important to have singly picked function type (...args: Paramters<T>) => ReturnType<T> for the most reasonable usability.

There are probably two ways to solve this. One way is like this PR to NormalizedPrecedure<T> inside MockInstance<T>. Another way which Jest does is to have a wrapper SpiedFunction<T> for MockInstance<(...args: Parameters<T>) => ReturnType<T>>.

I think what Jest does still have issues left (though I'm not sure if it's intentional or not). For example, SpiedFunction doesn't cover the case of vi.mocked helper, so it would fail the example from OP #6155. So, I thought it's more robust to go with the former approach.

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