Deprecate unused ButtonStyleButton.iconAlignment property (flutter#160023)

Fixes [Deprecate unused `ButtonStyleButton.iconAlignment`
property](flutter#159782)

Refactor done in flutter#158503 makes
`ButtonStyleButton.iconAlignment` redundant. In this PR I'm marking it
as deprecated without migration guide. However, it may possible to
remove it altogether.


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Author: TahaTesser

packages/flutter/lib/src/material/button_style_button.dart

@@ -86,6 +86,11 @@ abstract class ButtonStyleButton extends StatefulWidget {
     required this.clipBehavior,
     this.statesController,
     this.isSemanticButton = true,
+    @Deprecated(
+      'Remove this parameter as it is now ignored. '
+      'Use ButtonStyle.iconAlignment instead. '
+      'This feature was deprecated after v3.28.0-1.0.pre.',
+    )
     this.iconAlignment,
     this.tooltip,
     required this.child,
@@ -158,6 +163,11 @@ abstract class ButtonStyleButton extends StatefulWidget {
   final bool? isSemanticButton;
 
   /// {@macro flutter.material.ButtonStyleButton.iconAlignment}
+  @Deprecated(
+    'Remove this parameter as it is now ignored. '
+    'Use ButtonStyle.iconAlignment instead. '
+    'This feature was deprecated after v3.28.0-1.0.pre.',
+  )
   final IconAlignment? iconAlignment;
 
   /// Text that describes the action that will occur when the button is pressed or