Use pattern matching to avoid strange type annotations (#131964)

Addresses https://github.com/flutter/flutter/pull/131640#discussion_r1284861384

packages/flutter/lib/src/rendering/editable.dart

@@ -1918,16 +1918,14 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin,
   bool hitTestChildren(BoxHitTestResult result, { required Offset position }) {
     final Offset effectivePosition = position - _paintOffset;
     final InlineSpan? textSpan = _textPainter.text;
-    if (textSpan != null) {
-      final TextPosition textPosition = _textPainter.getPositionForOffset(effectivePosition);
-      final Object? span = textSpan.getSpanForPosition(textPosition);
-      if (span is HitTestTarget) {
+    switch (textSpan?.getSpanForPosition(_textPainter.getPositionForOffset(effectivePosition))) {
+      case final HitTestTarget span:
         result.add(HitTestEntry(span));
         return true;
-      }
-    }
+      case _:
         return hitTestInlineChildren(result, effectivePosition);
     }
+  }
 
   late TapGestureRecognizer _tap;
   late LongPressGestureRecognizer _longPress;

packages/flutter/lib/src/rendering/paragraph.dart

@@ -725,13 +725,14 @@ class RenderParagraph extends RenderBox with ContainerRenderObjectMixin<RenderBo
   @override
   bool hitTestChildren(BoxHitTestResult result, { required Offset position }) {
     final TextPosition textPosition = _textPainter.getPositionForOffset(position);
-    final Object? span = _textPainter.text!.getSpanForPosition(textPosition);
-    if (span is HitTestTarget) {
+    switch (_textPainter.text!.getSpanForPosition(textPosition)) {
+      case final HitTestTarget span:
         result.add(HitTestEntry(span));
         return true;
-    }
+      case _:
         return hitTestInlineChildren(result, position);
     }
+  }
 
   bool _needsClipping = false;
   ui.Shader? _overflowShader;