Create non-optional-returning as functions for superclasses/extended interfaces

[DougGregor]

AnyJavaObject provides an as method that performs a dynamic cast to another AnyJavaObject-conforming type, then returns an optional with either the casted type or nil to indicate failure.

When casting to the superclass type or the type of one of the interfaces that a type extends, the result will never be nil. Developers performing these upcasts will have to force-unwrap these results. For example:

let throwable: Throwable = ...
let object: JavaObject = throwable.as(JavaObject.self)!

As part of generating the Throwable Swift type, we could provide non-optional-returning overloads of as, e.g.,

@JavaClass("java.lang.Throwable")
struct Throwable {
  func as(_: JavaObject.Type) -> JavaObject { ... }
}

[AbdAlRahmanGad]

Hi @DougGregor,
Could you assign this issue to me?
Could you also point me to which file I should implement this change inside?