Tiny fix doc pointing to incorrect widget confusing the readers (#125394)

Just a one-word super tiny change, which I encounter today when playing with RawGestureDetector :)

The original doc says:

> For common gestures, use a [GestureRecognizer](https://api.flutter.dev/flutter/gestures/GestureRecognizer-class.html). [RawGestureDetector](https://api.flutter.dev/flutter/widgets/RawGestureDetector-class.html) is useful primarily when developing your own gesture recognizers.

However, for "common gestures", IMHO the doc wants to say `GestureDetector` (because that one has easy-to-use onTap, onLongPress etc). On the other hand, GestureRecognizer should be used together with RawGestureDetector and is a quite low-level thing, and for common gestures people seldom use it. So I guess here it is a typo.

packages/flutter/lib/src/widgets/gesture_detector.dart

@@ -1240,7 +1240,7 @@ class GestureDetector extends StatelessWidget {
 /// A widget that detects gestures described by the given gesture
 /// factories.
 ///
-/// For common gestures, use a [GestureRecognizer].
+/// For common gestures, use a [GestureDetector].
 /// [RawGestureDetector] is useful primarily when developing your
 /// own gesture recognizers.
 ///