Improve source file detection and tests

- Use SwiftPM-provided sourceFiles for filtering - Add Utils.swift with
URL descendant check - Update example to use Views/ instead of Folder/ -
Add test for non-included Swift file - Update .zed settings to disable
VSCode CSS language server

.zed/settings.json

@@ -0,0 +1,11 @@
+// Folder-specific settings
+//
+// For a full list of overridable settings, and general information on folder-specific settings,
+// see the documentation: https://zed.dev/docs/configuring-zed#settings-files
+{
+  "languages": {
+    "CSS": {
+      "language_servers": ["!vscode-css-language-server"]
+    }
+  }
+}