Fix chinese text is not selected by long press (#129320)

issue:#126652

 in Chinese text, word length is 1 and (position.offset == word.end) happens a lot.

Update if (position.offset >= word.end) to if (position.offset > word.end) to resolve the issue that Chinese characters are not selected.

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

@@ -1497,7 +1497,7 @@ class _SelectableFragment with Selectable, ChangeNotifier implements TextLayoutM
     assert(word.start >= range.start && word.end <= range.end);
     late TextPosition start;
     late TextPosition end;
-    if (position.offset >= word.end) {
+    if (position.offset > word.end) {
       start = end = TextPosition(offset: position.offset);
     } else {
       start = TextPosition(offset: word.start);

packages/flutter/test/rendering/paragraph_test.dart

@@ -821,6 +821,34 @@ void main() {
       expect(paintingContext.canvas.drawnRectPaint!.color, selectionColor);
     });
 
+// Regression test for https://github.com/flutter/flutter/issues/126652.
+    test('paints selection when tap at chinese character', () async {
+      final TestSelectionRegistrar registrar = TestSelectionRegistrar();
+      const Color selectionColor = Color(0xAF6694e8);
+      final RenderParagraph paragraph = RenderParagraph(
+        const TextSpan(text: '你好'),
+        textDirection: TextDirection.ltr,
+        registrar: registrar,
+        selectionColor: selectionColor,
+      );
+      layout(paragraph);
+      final MockPaintingContext paintingContext = MockPaintingContext();
+      paragraph.paint(paintingContext, Offset.zero);
+      expect(paintingContext.canvas.drawnRect, isNull);
+      expect(paintingContext.canvas.drawnRectPaint, isNull);
+
+      for (final Selectable selectable in (paragraph.registrar! as TestSelectionRegistrar).selectables) {
+        selectable.dispatchSelectionEvent(const SelectWordSelectionEvent(globalPosition: Offset(7, 0)));
+      }
+
+      paintingContext.canvas.clear();
+      paragraph.paint(paintingContext, Offset.zero);
+      expect(paintingContext.canvas.drawnRect,
+          const Rect.fromLTWH(0.0, 0.0, 14.0, 14.0));
+      expect(paintingContext.canvas.drawnRectPaint!.style, PaintingStyle.fill);
+      expect(paintingContext.canvas.drawnRectPaint!.color, selectionColor);
+    }, skip: isBrowser); // https://github.com/flutter/flutter/issues/61016
+
     test('getPositionForOffset works', () async {
       final RenderParagraph paragraph = RenderParagraph(const TextSpan(text: '1234567'), textDirection: TextDirection.ltr);
       layout(paragraph);