prevents sliver app bar from changing semantics tree when it is not necesaary (#61012)

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

@@ -258,26 +258,9 @@ abstract class RenderSliverPersistentHeader extends RenderSliver with RenderObje
     }
   }
 
-  /// Whether the [SemanticsNode]s associated with this [RenderSliver] should
-  /// be excluded from the semantic scrolling area.
-  ///
-  /// [RenderSliver]s that stay on the screen even though the user has scrolled
-  /// past them (e.g. a pinned app bar) should set this to true.
-  @protected
-  bool get excludeFromSemanticsScrolling => _excludeFromSemanticsScrolling;
-  bool _excludeFromSemanticsScrolling = false;
-  set excludeFromSemanticsScrolling(bool value) {
-    if (_excludeFromSemanticsScrolling == value)
-      return;
-    _excludeFromSemanticsScrolling = value;
-    markNeedsSemanticsUpdate();
-  }
-
   @override
   void describeSemanticsConfiguration(SemanticsConfiguration config) {
     super.describeSemanticsConfiguration(config);
-
-    if (_excludeFromSemanticsScrolling)
     config.addTagForChildren(RenderViewport.excludeFromScrolling);
   }
 
@@ -375,7 +358,6 @@ abstract class RenderSliverPinnedPersistentHeader extends RenderSliverPersistent
     final SliverConstraints constraints = this.constraints;
     final double maxExtent = this.maxExtent;
     final bool overlapsContent = constraints.overlap > 0.0;
-    excludeFromSemanticsScrolling = overlapsContent || (constraints.scrollOffset > maxExtent - minExtent);
     layoutChild(constraints.scrollOffset, maxExtent, overlapsContent: overlapsContent);
     final double effectiveRemainingPaintExtent = math.max(0, constraints.remainingPaintExtent - constraints.overlap);
     final double layoutExtent = (maxExtent - constraints.scrollOffset).clamp(0.0, effectiveRemainingPaintExtent) as double;
@@ -575,7 +557,6 @@ abstract class RenderSliverFloatingPersistentHeader extends RenderSliverPersiste
     } else {
       _effectiveScrollOffset = constraints.scrollOffset;
     }
-    excludeFromSemanticsScrolling = _effectiveScrollOffset <= constraints.scrollOffset;
     final bool overlapsContent = _effectiveScrollOffset < constraints.scrollOffset;
 
     layoutChild(

packages/flutter/test/material/app_bar_test.dart

@@ -1645,9 +1645,6 @@ void main() {
                     flags: <SemanticsFlag>[SemanticsFlag.scopesRoute],
                     children: <TestSemantics>[
                       TestSemantics(
-                        children: <TestSemantics>[
-                          TestSemantics(
-                            flags: <SemanticsFlag>[SemanticsFlag.hasImplicitScrolling],
                         children: <TestSemantics>[
                           TestSemantics(
                             children: <TestSemantics>[
@@ -1661,7 +1658,8 @@ void main() {
                               ),
                             ],
                           ),
-                            ],
+                          TestSemantics(
+                            flags: <SemanticsFlag>[SemanticsFlag.hasImplicitScrolling],
                           ),
                         ],
                       ),

packages/flutter/test/widgets/sliver_semantics_test.dart

@@ -78,13 +78,6 @@ void _tests() {
             children: <TestSemantics>[
               TestSemantics(
                 id: 2,
-                children: <TestSemantics>[
-                  TestSemantics(
-                    id: 9,
-                    flags: <SemanticsFlag>[
-                      SemanticsFlag.hasImplicitScrolling,
-                    ],
-                    actions: <SemanticsAction>[SemanticsAction.scrollUp],
                 children: <TestSemantics>[
                   TestSemantics(
                     id: 7,
@@ -100,6 +93,13 @@ void _tests() {
                       ),
                     ],
                   ),
+                  TestSemantics(
+                    id: 9,
+                    flags: <SemanticsFlag>[
+                      SemanticsFlag.hasImplicitScrolling,
+                    ],
+                    actions: <SemanticsAction>[SemanticsAction.scrollUp],
+                    children: <TestSemantics>[
                       TestSemantics(
                         id: 3,
                         label: 'Item 0',
@@ -225,16 +225,6 @@ void _tests() {
             children: <TestSemantics>[
               TestSemantics(
                 id: 2,
-                children: <TestSemantics>[
-                  TestSemantics(
-                    id: 9,
-                    flags: <SemanticsFlag>[
-                      SemanticsFlag.hasImplicitScrolling,
-                    ],
-                    actions: <SemanticsAction>[
-                      SemanticsAction.scrollUp,
-                      SemanticsAction.scrollDown,
-                    ],
                 children: <TestSemantics>[
                   TestSemantics(
                     id: 7,
@@ -250,6 +240,16 @@ void _tests() {
                       ),
                     ],
                   ),
+                  TestSemantics(
+                    id: 9,
+                    flags: <SemanticsFlag>[
+                      SemanticsFlag.hasImplicitScrolling,
+                    ],
+                    actions: <SemanticsAction>[
+                      SemanticsAction.scrollUp,
+                      SemanticsAction.scrollDown,
+                    ],
+                    children: <TestSemantics>[
                       TestSemantics(
                         id: 3,
                         label: 'Item 0',