Add DetailCalloutAccessory

This was authored by @pauljohanneskraft in the comment at pauljohanneskraft#46 (comment)

Sources/Annotations/DetailCalloutAccessory.swift

@@ -0,0 +1,68 @@
+//
+//  DetailCalloutAccessory.swift
+//  Map
+//
+//  Created by Darron Schall on 10/4/23.
+//
+
+#if !os(watchOS)
+
+import Foundation
+import MapKit
+import SwiftUI
+
+private struct DetailCalloutAccessory<Annotation: MapAnnotation, Content: View>: MapAnnotation {
+
+    // MARK: Static Functions
+
+    static func registerView(on mapView: MKMapView) {
+        Annotation.registerView(on: mapView)
+    }
+
+    // MARK: Stored Properties
+
+    private let wrappedAnnotation: Annotation
+    private let content: () -> Content
+
+    // MARK: Computed Properties
+
+    var annotation: MKAnnotation {
+        wrappedAnnotation.annotation
+    }
+
+    // MARK: Initialization
+
+    init(_ annotation: Annotation, @ViewBuilder content: @escaping () -> Content) {
+        self.wrappedAnnotation = annotation
+        self.content = content
+    }
+
+    // MARK: Methods
+
+    func view(for mapView: MKMapView) -> MKAnnotationView? {
+        guard let view = wrappedAnnotation.view(for: mapView) else {
+            return nil
+        }
+
+        if Content.self != EmptyView.self {
+            view.canShowCallout = true
+            view.detailCalloutAccessoryView = NativeHostingController(rootView: content()).view
+        } else {
+            view.canShowCallout = false
+            view.detailCalloutAccessoryView = nil
+        }
+
+        return view
+    }
+
+}
+
+extension MapAnnotation {
+
+    public func detailCalloutAccessory<Content: View>(@ViewBuilder content: @escaping () -> Content) -> some MapAnnotation {
+        DetailCalloutAccessory(self, content: content)
+    }
+
+}
+
+#endif