Crash occurs when diffing two `LocalizedStringKeys` with special interpolations

[daltonclaybrook]

Describe the bug
Passing a LocalizedStringKey constructed with basic string interpolation works correctly. For example, the following code works as you would expect:

let name = "Dalton"
let control: LocalizedStringKey = "Static string"
let success: LocalizedStringKey = "Hello, \(name)!"

// This prints:
// - "Static string"
// + "Hello, Dalton!"
print(diff(control, success) ?? "No diff")

However, passing a LocalizedStringKey that uses any of the other variations of string interpolation supported by LocalizedStringKey results in a crash:

let control: LocalizedStringKey = "Static string"
let crash1: LocalizedStringKey = "Date: \(Date(), style: .date)"
let crash2: LocalizedStringKey = "Date range: \(Date.distantPast...Date.distantFuture)"
let crash3: LocalizedStringKey = "Time: \(Duration.seconds(10), format: .time(pattern: .minuteSecond))"

print(diff(control, crash1) ?? "No diff") // crash!
print(diff(control, crash2) ?? "No diff") // crash!
print(diff(control, crash3) ?? "No diff") // crash!

The crash (SIGABRT) occurs on this line:

swift-custom-dump/Sources/CustomDump/Conformances/SwiftUI.swift

Line 59 in c2012e1

Array(Mirror(reflecting: children[0].value).children)[0].value as! (Any, Formatter?)

The console output:

Could not cast value of type 'SwiftUI.LocalizedStringKey.FormatArgument.Token' (0x1fea477e8) to 'NSFormatter' (0x1fd708ed8).
2023-09-02 19:11:54.584602-0500 dump-bug[32884:11397570] Could not cast value of type 'SwiftUI.LocalizedStringKey.FormatArgument.Token' (0x1fea477e8) to 'NSFormatter' (0x1fd708ed8).

Expected behavior
I expect that the above code would not result in a crash and would instead print an appropriate diff between the provided strings.

Environment

• swift-custom-dump version: 1.0.0
• Xcode Version 14.3.1 (14E300c)
• Swift version 5.8.1 (swiftlang-5.8.0.124.5 clang-1403.0.22.11.100)
• OS: macOS 13.4.1 (c) (22F770820d) and iOS 16.4