Fixes example snippet of AnyHashable

[valeriyvan]

Otherwise, print(descriptions[AnyHashable(43)]) prints an Int8, not nil.

This PR fixes example snippet in comments making it working as described.

n/a

[rjmccall]

@airspeedswift Is this expected behavior for AnyHashable?

[jckarter]

It is.

[jckarter]

It might be more illustrative to keep the descriptions[AnyHashable(43)] example here, and update the 'prints "nil"' comment to show the expected behavior.

[natecook1000]

@jckarter What types are fungible like this? It seems to work for numeric types as long as there's an exact precision match (i.e. you can get 2.25 out as a Float, but not 2.2), but trying to get a string out as a character fails.

[jckarter]

@natecook1000 AnyHashable should behave this way for any types that are transitively as?-castable, so you can get a String out as an NSString and v.v., an Array<T> as an NSArray, and so on. The standard library integer and floating-point types as well as CGFloat and Decimal all bridge to NSNumber, and NSNumber bridges back to any of those types if the value is exactly representable.

[CodaFi]

I think this change is good to take as-is.

@swift-ci please smoke test and merge