Same cursor offset within lines for all TextAffinities to prevent cursor shifting/moving. (#23485)

bin/internal/goldens.version

-afef1dc571f94a41751917d3946defba782335f7
+055a75c5a63bf2b2c5142b38b88829593908fd10

packages/flutter/lib/src/painting/text_painter.dart

@@ -421,7 +421,7 @@ class TextPainter {
       return null;
     final TextBox box = boxes[0];
     final double caretEnd = box.end;
-    final double dx = box.direction == TextDirection.rtl ? caretEnd : caretEnd - caretPrototype.width;
+    final double dx = box.direction == TextDirection.rtl ? caretEnd - caretPrototype.width : caretEnd;
     return Offset(dx, box.top);
   }
 

packages/flutter/test/material/text_field_test.dart

@@ -741,6 +741,11 @@ void main() {
     final Offset firstPos = textOffsetToPosition(tester, testValue.indexOf('First'));
     final Offset secondPos = textOffsetToPosition(tester, testValue.indexOf('Second'));
     final Offset thirdPos = textOffsetToPosition(tester, testValue.indexOf('Third'));
+    final Offset middleStringPos = textOffsetToPosition(tester, testValue.indexOf('irst'));
+    expect(firstPos.dx, 0);
+    expect(secondPos.dx, 0);
+    expect(thirdPos.dx, 0);
+    expect(middleStringPos.dx, 34);
     expect(firstPos.dx, secondPos.dx);
     expect(firstPos.dx, thirdPos.dx);
     expect(firstPos.dy, lessThan(secondPos.dy));
@@ -823,6 +828,8 @@ void main() {
     // Check that the last line of text is not displayed.
     final Offset firstPos = textOffsetToPosition(tester, kMoreThanFourLines.indexOf('First'));
     final Offset fourthPos = textOffsetToPosition(tester, kMoreThanFourLines.indexOf('Fourth'));
+    expect(firstPos.dx, 0);
+    expect(fourthPos.dx, 0);
     expect(firstPos.dx, fourthPos.dx);
     expect(firstPos.dy, lessThan(fourthPos.dy));
     expect(inputBox.hitTest(HitTestResult(), position: inputBox.globalToLocal(firstPos)), isTrue);