Prefer checking module availability over the os check (gonzalezreal#268)

* refactor: prefer checking module availability over the os check for `AssetImageProvider`

* refactor: prefer checking module availability over the os check for `Color+RGBA`

Author: MojtabaHs

Sources/MarkdownUI/Extensibility/AssetImageProvider.swift

@@ -38,7 +38,7 @@ public struct AssetImageProvider: ImageProvider {
   }
 
   private func image(url: URL) -> PlatformImage? {
-    #if os(macOS)
+    #if canImport(AppKit)
       if let bundle, bundle != .main {
         return bundle.image(forResource: self.name(url))
       } else {
@@ -61,15 +61,15 @@ extension ImageProvider where Self == AssetImageProvider {
 
 #if canImport(UIKit)
   private typealias PlatformImage = UIImage
-#elseif os(macOS)
+#elseif canImport(AppKit)
   private typealias PlatformImage = NSImage
 #endif
 
 extension Image {
   fileprivate init(platformImage: PlatformImage) {
     #if canImport(UIKit)
       self.init(uiImage: platformImage)
-    #elseif os(macOS)
+    #elseif canImport(AppKit)
       self.init(nsImage: platformImage)
     #endif
   }

Sources/MarkdownUI/Utility/Color+RGBA.swift

@@ -17,7 +17,7 @@ extension Color {
   ///   - light: The light appearance color value.
   ///   - dark: The dark appearance color value.
   public init(light: @escaping @autoclosure () -> Color, dark: @escaping @autoclosure () -> Color) {
-    #if os(macOS)
+    #if canImport(AppKit)
       self.init(
         nsColor: .init(name: nil) { appearance in
           if appearance.bestMatch(from: [.aqua, .darkAqua]) == .aqua {