Implement switch expressions in dev/ (#139048)

I previously made a PR (#136140) that used `switch` expressions to make some parts of the Flutter codebase easier to understand. It was assigned to the framework team, and @christopherfujino let me know that it was too large to effectively review and recommended breaking it up into smaller pull requests.

Here's a PR that only targets files in the `dev/` directory. Hopefully this will be easier to work with!

(solves issue https://github.com/flutter/flutter/issues/136139)

dev/tools/vitool/lib/vitool.dart

@@ -152,19 +152,13 @@ class PathCommandAnimation {
   }
 
   String toDart() {
-    String dartCommandClass;
-    switch (type) {
-      case 'M':
-        dartCommandClass = '_PathMoveTo';
-      case 'C':
-        dartCommandClass = '_PathCubicTo';
-      case 'L':
-        dartCommandClass = '_PathLineTo';
-      case 'Z':
-        dartCommandClass = '_PathClose';
-      default:
-        throw Exception('unsupported path command: $type');
-    }
+    final String dartCommandClass = switch (type) {
+      'M' => '_PathMoveTo',
+      'C' => '_PathCubicTo',
+      'L' => '_PathLineTo',
+      'Z' => '_PathClose',
+      _ => throw Exception('unsupported path command: $type'),
+    };
     final StringBuffer sb = StringBuffer();
     sb.write('${kIndent * 4}const $dartCommandClass(\n');
     for (final List<Point<double>> pointFrames in points) {