Fix handling backspace on macos with text selection (#49760)

Fixes #46150 by catching both the delete and backspace keys, rather than just the delete key.

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

@@ -431,12 +431,17 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
     LogicalKeyboardKey.arrowDown,
   };
 
+  static final Set<LogicalKeyboardKey> _deleteKeys = <LogicalKeyboardKey>{
+    LogicalKeyboardKey.delete,
+    LogicalKeyboardKey.backspace,
+  };
+
   static final Set<LogicalKeyboardKey> _shortcutKeys = <LogicalKeyboardKey>{
     LogicalKeyboardKey.keyA,
     LogicalKeyboardKey.keyC,
     LogicalKeyboardKey.keyV,
     LogicalKeyboardKey.keyX,
-    LogicalKeyboardKey.delete,
+    ..._deleteKeys,
   };
 
   static final Set<LogicalKeyboardKey> _nonModifierKeys = <LogicalKeyboardKey>{
@@ -491,7 +496,7 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
       // _handleShortcuts depends on being started in the same stack invocation
       // as the _handleKeyEvent method
       _handleShortcuts(key);
-    } else if (key == LogicalKeyboardKey.delete) {
+    } else if (_deleteKeys.contains(key)) {
       _handleDelete();
     }
   }

packages/flutter/test/widgets/editable_text_test.dart

@@ -3738,6 +3738,51 @@ void main() {
       reason: 'on $platform',
     );
     expect(controller.text, isEmpty, reason: 'on $platform');
+
+    /// Paste and Select All
+    await sendKeys(
+      tester,
+      <LogicalKeyboardKey>[
+        LogicalKeyboardKey.keyV,
+        LogicalKeyboardKey.keyA,
+      ],
+      shortcutModifier: true,
+      platform: platform,
+    );
+
+    expect(
+      selection,
+      equals(
+        const TextSelection(
+          baseOffset: 0,
+          extentOffset: testText.length,
+          affinity: TextAffinity.downstream,
+        ),
+      ),
+      reason: 'on $platform',
+    );
+    expect(controller.text, equals(testText), reason: 'on $platform');
+
+    // Backspace
+    await sendKeys(
+      tester,
+      <LogicalKeyboardKey>[
+        LogicalKeyboardKey.delete,
+      ],
+      platform: platform,
+    );
+    expect(
+      selection,
+      equals(
+        const TextSelection(
+          baseOffset: 0,
+          extentOffset: 72,
+          affinity: TextAffinity.downstream,
+        ),
+      ),
+      reason: 'on $platform',
+    );
+    expect(controller.text, isEmpty, reason: 'on $platform');
   }
 
   testWidgets('keyboard text selection works as expected on linux', (WidgetTester tester) async {