Remove custom NSErrorException in favor of built-in ObjCErrorException

[darronschall]

Instead of introducing our own NSErrorException to propagate NSErrors to Swift (that I introduced in #598), we change on approach to instead rely on the built-in (albeit internal) ObjCErrorException via https://github.com/JetBrains/kotlin/blob/b05604058fa3c480030267629cc70cf180a1263d/kotlin-native/runtime/src/main/kotlin/kotlin/native/internal/ObjCExportUtils.kt#L274

Previously, we needed to create a helper on the Swift side of things to extract the nested NSError details when throwing NSErrorExceptions in our code:

extension Error {
    var wrappedNSError: NSError? {
        let kotlinException = (self as NSError).userInfo["KotlinException"] as? KotlinException
        let nsErrorException = kotlinException as? NSErrorException
        return nsErrorException?.nsError as? NSError
    }
}

Downstream users had to rely on the helper extension to read the error details:

do {
    //
} catch {
    if let wrappedError = error.wrappedNSError {
        print("wrappedError domain: \(wrappedError.domain)")
        // etc.
    }
}

With this updated approach leveraging ObjCErrorException, the error in the Swift catch block is already an NSError containing the correct error information. We can simply read the data from it, no Error extension required:

do {
    //
} catch {
    let nsError = error as NSError
    print("nsError domain: \(nsError.domain)")
}

This simplifies things for downstream users.

Using this updated approach, here's what I see when purposefully generating an error scenario (calling registerFont() on the same font multiple times):

do {
    try fontResource.registerFont()
    try fontResource.registerFont() // force a failure to demonstrate improved error handling
} catch {
    let nsError = error as NSError
    print("nsError: \(nsError)")
}

nsError: Error Domain=com.apple.CoreText.CTFontManagerErrorDomain Code=105 "Font registration was unsuccessful." UserInfo={NSLocalizedDescription=Font registration was unsuccessful., CTFontManagerErrorFontURLs=(
    "[trimmed]/OpenSans-Regular.ttf"
)}