Add ComposableView for custom platform composables

Author: colemancda

AndroidSwiftUICore/Sources/AndroidSwiftUICore/Primitives/ComposableView.swift

@@ -0,0 +1,62 @@
+//
+//  ComposableView.swift
+//  AndroidSwiftUICore
+//
+//  The library's escape hatch for custom platform UI — the counterpart to
+//  UIKit's `UIViewRepresentable`. Because a `@Composable` (or an Android
+//  `View`) can never be authored in Swift, the seam is a *named registry*:
+//  Kotlin registers `name → composable` factories once at startup, and this
+//  view references one by name, forwarding typed props and an optional slot of
+//  SwiftUI child content.
+//
+//  Kotlin side:
+//
+//      ComposableRegistry.register("RatingBar") { props, _ ->
+//          AndroidView(factory = { RatingBar(it) }, update = {
+//              it.rating = (props["rating"] as? JsonPrimitive)?.floatOrNull ?: 0f
+//          })
+//      }
+//
+//  Swift side:
+//
+//      ComposableView("RatingBar", props: ["rating": 3.5, "max": 5])
+//
+//  A factory that wraps an Android-only `View` (maps, WebView, an ad SDK) uses
+//  Compose's own `AndroidView` inside the registered composable — so arbitrary
+//  custom Android views compose into a SwiftUI tree. An unregistered name
+//  renders a visible diagnostic rather than failing silently.
+//
+
+public struct ComposableView<Content: View>: View {
+
+    internal let name: String
+    internal let props: [String: PropValue]
+    internal let content: Content
+
+    public init(_ name: String, props: [String: PropValue] = [:], @ViewBuilder content: () -> Content) {
+        self.name = name
+        self.props = props
+        self.content = content()
+    }
+
+    public typealias Body = Never
+}
+
+public extension ComposableView where Content == EmptyView {
+    init(_ name: String, props: [String: PropValue] = [:]) {
+        self.init(name, props: props) { EmptyView() }
+    }
+}
+
+extension ComposableView: PrimitiveView {
+    public func _render(in context: ResolveContext) -> RenderNode {
+        var props = self.props
+        props["name"] = .string(name)   // reserved: identifies the registered factory
+        return RenderNode(
+            type: "Composable",
+            id: context.path,
+            props: props,
+            children: Evaluator.resolveChildren(content, context.descending("content"))
+        )
+    }
+}