Fix right alignment TWB longestLine (#54234)

Fixes an alignment bug seen when using both TextWidthBasis.longestLine and TextAlign.right.

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

@@ -564,7 +564,7 @@ class TextPainter {
     _paragraph.layout(ui.ParagraphConstraints(width: maxWidth));
     if (minWidth != maxWidth) {
       final double newWidth = maxIntrinsicWidth.clamp(minWidth, maxWidth) as double;
-      if (newWidth != width) {
+      if (newWidth != _applyFloatingPointHack(_paragraph.width)) {
         _paragraph.layout(ui.ParagraphConstraints(width: newWidth));
       }
     }

packages/flutter/test/widgets/text_test.dart

@@ -800,6 +800,56 @@ void main() {
     expect(textSizeLongestLine.height, equals(fontHeight * 2));
   }, skip: isBrowser);  // TODO(yjbanov): https://github.com/flutter/flutter/issues/44020
 
+  testWidgets('textWidthBasis with textAlign still obeys parent alignment', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Scaffold(
+          body: Center(
+            child: Column(
+              mainAxisSize: MainAxisSize.min,
+              crossAxisAlignment: CrossAxisAlignment.start,
+              children: const <Widget>[
+                Text(
+                  'LEFT ALIGNED, PARENT',
+                  textAlign: TextAlign.left,
+                  textWidthBasis: TextWidthBasis.parent,
+                ),
+                Text(
+                  'RIGHT ALIGNED, PARENT',
+                  textAlign: TextAlign.right,
+                  textWidthBasis: TextWidthBasis.parent,
+                ),
+                Text(
+                  'LEFT ALIGNED, LONGEST LINE',
+                  textAlign: TextAlign.left,
+                  textWidthBasis: TextWidthBasis.longestLine,
+                ),
+                Text(
+                  'RIGHT ALIGNED, LONGEST LINE',
+                  textAlign: TextAlign.right,
+                  textWidthBasis: TextWidthBasis.longestLine,
+                ),
+              ],
+            ),
+          ),
+        ),
+      ),
+    );
+
+    // All Texts have the same horizontal alignment.
+    final double offsetX = tester.getTopLeft(find.text('LEFT ALIGNED, PARENT')).dx;
+    expect(tester.getTopLeft(find.text('RIGHT ALIGNED, PARENT')).dx, equals(offsetX));
+    expect(tester.getTopLeft(find.text('LEFT ALIGNED, LONGEST LINE')).dx, equals(offsetX));
+    expect(tester.getTopLeft(find.text('RIGHT ALIGNED, LONGEST LINE')).dx, equals(offsetX));
+
+    // All Texts are less than or equal to the width of the Column.
+    final double width = tester.getSize(find.byType(Column)).width;
+    expect(tester.getSize(find.text('LEFT ALIGNED, PARENT')).width, lessThan(width));
+    expect(tester.getSize(find.text('RIGHT ALIGNED, PARENT')).width, lessThan(width));
+    expect(tester.getSize(find.text('LEFT ALIGNED, LONGEST LINE')).width, lessThan(width));
+    expect(tester.getSize(find.text('RIGHT ALIGNED, LONGEST LINE')).width, equals(width));
+  }, skip: isBrowser);  // TODO(yjbanov): https://github.com/flutter/flutter/issues/44020
+
   testWidgets('Paragraph.getBoxesForRange returns nothing when selection range is zero length', (WidgetTester tester) async {
     final ui.ParagraphBuilder builder = ui.ParagraphBuilder(ui.ParagraphStyle());
     builder.addText('hello');