Fix ScrollPosition overscroll precision error (#127321)

## Description

This PR fixes a precision error in ~~`ClampingScrollPhysics`~~ `ScrollPosition` that leads to `StretchingOverscrollIndicator` stretching its content unexpectedly in some devices (see  https://github.com/flutter/flutter/issues/126561 where this is visible in `TabBarView` and the test added in this PR where it reproduces with a `PageView`).

~~This PR also contains a change to `nested_scroll_view.dart` because the first change (the one in `ClampingScrollPhysics`)  breaks the precision error test added by https://github.com/flutter/flutter/pull/87801.~~

## Related Issue

Fixes https://github.com/flutter/flutter/issues/126561

## Tests

Adds 1 test.

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

@@ -368,7 +368,7 @@ abstract class ScrollPosition extends ViewportOffset with ScrollMetrics {
         notifyListeners();
         didUpdateScrollPositionBy(pixels - oldPixels);
       }
-      if (overscroll != 0.0) {
+      if (overscroll.abs() > precisionErrorTolerance) {
         didOverscrollBy(overscroll);
         return overscroll;
       }

packages/flutter/test/widgets/page_view_test.dart

@@ -1203,4 +1203,46 @@ void main() {
     await tester.pump();
     expect(tester.takeException(), isNull);
   });
+
+  testWidgets('PageView content should not be stretched on precision error', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/126561.
+    final PageController controller = PageController();
+
+    const double pixel6EmulatorWidth = 411.42857142857144;
+
+    await tester.pumpWidget(MaterialApp(
+      theme: ThemeData(useMaterial3: true),
+      home: Center(
+        child: SizedBox(
+          width: pixel6EmulatorWidth,
+          child: PageView(
+            controller: controller,
+            physics: const PageScrollPhysics().applyTo(const ClampingScrollPhysics()),
+            children: const <Widget>[
+              Center(child: Text('First Page')),
+              Center(child: Text('Second Page')),
+              Center(child: Text('Third Page')),
+            ],
+          ),
+        ),
+      ),
+    ));
+
+    controller.animateToPage(2, duration: const Duration(milliseconds: 300), curve: Curves.ease);
+    await tester.pumpAndSettle();
+
+    final Finder transformFinder = find.descendant(of: find.byType(PageView), matching: find.byType(Transform));
+    expect(transformFinder, findsOneWidget);
+
+    // Get the Transform widget that stretches the PageView.
+    final Transform transform = tester.firstWidget<Transform>(
+      find.descendant(
+        of: find.byType(PageView),
+        matching: find.byType(Transform),
+      ),
+    );
+
+    // Check the stretch factor in the first element of the transform matrix.
+    expect(transform.transform.storage.first, 1.0);
+  });
 }