Deprecate MaterialButtonWithIconMixin (#99088)

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

@@ -422,7 +422,7 @@ class _MouseCursor extends MaterialStateMouseCursor {
   String get debugDescription => 'ButtonStyleButton_MouseCursor';
 }
 
-/// A widget to pad the area around a [MaterialButton]'s inner [Material].
+/// A widget to pad the area around a [ButtonStyleButton]'s inner [Material].
 ///
 /// Redirect taps that occur in the padded area around the child to the center
 /// of the child. This increases the size of the button and the button's

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

@@ -457,9 +457,15 @@ class MaterialButton extends StatelessWidget {
   }
 }
 
-/// The type of [MaterialButton]s created with [RaisedButton.icon], [FlatButton.icon],
-/// and [OutlineButton.icon].
+/// The type of [MaterialButton]s created with RaisedButton.icon, FlatButton.icon,
+/// and OutlineButton.icon.
 ///
 /// This mixin only exists to give the "label and icon" button widgets a distinct
 /// type for the sake of [ButtonTheme].
+@Deprecated(
+  'This was used to differentiate types of FlatButton, RaisedButton, and OutlineButton in ButtonTheme. '
+  'These buttons have been replaced with TextButton, ElevatedButton, and OutlinedButton, each of which have their own respective themes now. '
+  'Use one of these button classes instead. '
+  'This feature was deprecated after v2.11.0-0.0.pre.',
+)
 mixin MaterialButtonWithIconMixin { }