Update the site creation loading illustration (#25761)

* Swap the site creation loading illustration

Replaces the dated illustration on the "Almost done" site-assembly screen with design's current browser-windows artwork (CMM-2138). Vector PDFs for light and dark, scaled from the 602pt artboard to a 220pt display width.

* Add SwiftUI previews for the site assembly screen

Light and dark `#Preview`s that render `SiteAssemblyContentView` in its `.inProgress` state, so the loading illustration can be reviewed in isolation.

Author: jkmassel

WordPress/Classes/ViewRelated/Site Creation/Final Assembly/SiteAssemblyContentView.swift

@@ -1,4 +1,5 @@
 import UIKit
+import SwiftUI
 import Gridicons
 import WordPressShared
 import WordPressUI
@@ -603,3 +604,29 @@ private enum Strings {
         )
     }
 }
+
+// MARK: - Previews
+
+/// Renders the in-progress assembly screen in isolation so the loading illustration can be
+/// reviewed without driving the whole site-creation flow. The view is laid out in `.idle`
+/// first (which hides the completion labels) and then advanced to `.inProgress`.
+private func makeSiteAssemblyLoadingPreview(style: UIUserInterfaceStyle) -> UIViewController {
+    let contentView = SiteAssemblyContentView(siteCreator: SiteCreator())
+    contentView.frame = CGRect(x: 0, y: 0, width: 402, height: 874)
+    contentView.status = .idle
+    contentView.layoutIfNeeded()
+    contentView.status = .inProgress
+
+    let controller = UIViewController()
+    controller.overrideUserInterfaceStyle = style
+    controller.view = contentView
+    return controller
+}
+
+#Preview("Site Assembly – Light") {
+    makeSiteAssemblyLoadingPreview(style: .light)
+}
+
+#Preview("Site Assembly – Dark") {
+    makeSiteAssemblyLoadingPreview(style: .dark)
+}

WordPress/Resources/AppImages.xcassets/site-creation-loading.imageset/Contents.json

@@ -27,5 +27,8 @@
   "info" : {
     "version" : 1,
     "author" : "xcode"
+  },
+  "properties" : {
+    "preserves-vector-representation" : true
   }
 }