DiagnosticEngine: Print the ID of the wrapped, not wrapper, diagnostic

[AnthonyLatsis]

-debug-diagnostic-names always favors the effective ID of an emitted diagnostic. This is not ideal for wrapper diagnostics because they are an implementation detail of the diagnostic engine:

protocol P {
    func test(_: () -> Void)
}

struct S: P {
    func test(_: @Sendable () -> Void) {}
}

warning: sendability of function types in instance method 'test' does not match requirement in protocol 'P'; this is an error in the Swift 6 language mode [error_in_swift_lang_mode]

What is most relevant to both a compiler engineer and developer is the identity of the underlying diagnostic the engine was instructed to emit by a client.

[AnthonyLatsis]

@swift-ci please smoke test macOS

[AnthonyLatsis]

@swift-ci please smoke test Linux

[AnthonyLatsis]

@swift-ci please smoke test Windows