[chore]: move ViewEnvironment's EnvironmentValues key to the ViewEnvironment module (#266)

Author: n8chur

WorkflowSwiftUIExperimental/Sources/EnvironmentValues+ViewEnvironment.swift renamed to ViewEnvironment/Sources/EnvironmentValues+ViewEnvironment.swift

@@ -14,16 +14,19 @@
  * limitations under the License.
  */
 
-import SwiftUI
-import WorkflowUI
+#if canImport(SwiftUI)
 
-private struct ViewEnvironmentKey: EnvironmentKey {
-    static let defaultValue: ViewEnvironment = .empty
-}
+import SwiftUI
 
-public extension EnvironmentValues {
-    var viewEnvironment: ViewEnvironment {
+extension EnvironmentValues {
+    public var viewEnvironment: ViewEnvironment {
         get { self[ViewEnvironmentKey.self] }
         set { self[ViewEnvironmentKey.self] = newValue }
     }
+
+    private struct ViewEnvironmentKey: EnvironmentKey {
+        static let defaultValue: ViewEnvironment = .empty
+    }
 }
+
+#endif