Migrate to Theme.brightnessOf method (#163950)

Refactor: Migrate to Theme.brightnessOf method
fixes: #163837

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [ ] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

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

@@ -298,7 +298,7 @@ class _BottomAppBarDefaultsM2 extends BottomAppBarTheme {
 
   @override
   Color? get color =>
-      Theme.of(context).brightness == Brightness.dark ? Colors.grey[800]! : Colors.white;
+      Theme.brightnessOf(context) == Brightness.dark ? Colors.grey[800]! : Colors.white;
 
   @override
   Color? get surfaceTintColor => Theme.of(context).colorScheme.surfaceTint;

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

@@ -1465,7 +1465,7 @@ class _DropdownButtonState<T> extends State<DropdownButton<T>> with WidgetsBindi
 
   Color get _iconColor {
     // These colors are not defined in the Material Design spec.
-    final Brightness brightness = Theme.of(context).brightness;
+    final Brightness brightness = Theme.brightnessOf(context);
     if (_enabled) {
       return widget.iconEnabledColor ??
           switch (brightness) {

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

@@ -173,7 +173,7 @@ class _ExpandIconState extends State<ExpandIcon> with SingleTickerProviderStateM
       return widget.color!;
     }
 
-    return switch (Theme.of(context).brightness) {
+    return switch (Theme.brightnessOf(context)) {
       Brightness.light => Colors.black54,
       Brightness.dark => Colors.white60,
     };

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

@@ -1002,7 +1002,7 @@ class _IconButtonM3 extends ButtonStyleButton {
   ButtonStyle? themeStyleOf(BuildContext context) {
     final IconThemeData iconTheme = IconTheme.of(context);
     final bool isDefaultSize = iconTheme.size == const IconThemeData.fallback().size;
-    final bool isDefaultColor = identical(iconTheme.color, switch (Theme.of(context).brightness) {
+    final bool isDefaultColor = identical(iconTheme.color, switch (Theme.brightnessOf(context)) {
       Brightness.light => kDefaultIconDarkColor,
       Brightness.dark => kDefaultIconLightColor,
     });

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

@@ -5070,7 +5070,7 @@ class _InputDecoratorDefaultsM2 extends InputDecorationTheme {
 
   @override
   Color? get fillColor => MaterialStateColor.resolveWith((Set<MaterialState> states) {
-    return switch ((Theme.of(context).brightness, states.contains(MaterialState.disabled))) {
+    return switch ((Theme.brightnessOf(context), states.contains(MaterialState.disabled))) {
       (Brightness.dark, true) => const Color(0x0DFFFFFF), //  5% white
       (Brightness.dark, false) => const Color(0x1AFFFFFF), // 10% white
       (Brightness.light, true) => const Color(0x05000000), //  2% black
@@ -5086,7 +5086,7 @@ class _InputDecoratorDefaultsM2 extends InputDecorationTheme {
     if (states.contains(MaterialState.focused)) {
       return Theme.of(context).colorScheme.primary;
     }
-    return switch (Theme.of(context).brightness) {
+    return switch (Theme.brightnessOf(context)) {
       Brightness.dark => Colors.white70,
       Brightness.light => Colors.black45,
     };
@@ -5100,7 +5100,7 @@ class _InputDecoratorDefaultsM2 extends InputDecorationTheme {
     if (states.contains(MaterialState.focused)) {
       return Theme.of(context).colorScheme.primary;
     }
-    return switch (Theme.of(context).brightness) {
+    return switch (Theme.brightnessOf(context)) {
       Brightness.dark => Colors.white70,
       Brightness.light => Colors.black45,
     };
@@ -5117,7 +5117,7 @@ class _InputDecoratorDefaultsM2 extends InputDecorationTheme {
     if (states.contains(MaterialState.focused)) {
       return Theme.of(context).colorScheme.primary;
     }
-    return switch (Theme.of(context).brightness) {
+    return switch (Theme.brightnessOf(context)) {
       Brightness.dark => Colors.white70,
       Brightness.light => Colors.black45,
     };

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

@@ -430,7 +430,7 @@ class _StepperState extends State<Stepper> with TickerProviderStateMixin {
   }
 
   bool _isDark() {
-    return Theme.of(context).brightness == Brightness.dark;
+    return Theme.brightnessOf(context) == Brightness.dark;
   }
 
   bool _isLabel() {
@@ -593,7 +593,7 @@ class _StepperState extends State<Stepper> with TickerProviderStateMixin {
       );
     }
 
-    final Color cancelColor = switch (Theme.of(context).brightness) {
+    final Color cancelColor = switch (Theme.brightnessOf(context)) {
       Brightness.light => Colors.black54,
       Brightness.dark => Colors.white70,
     };

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

@@ -2630,7 +2630,7 @@ class _TabsDefaultsM2 extends TabBarThemeData {
 
   final BuildContext context;
   late final ColorScheme _colors = Theme.of(context).colorScheme;
-  late final bool isDark = Theme.of(context).brightness == Brightness.dark;
+  late final bool isDark = Theme.brightnessOf(context) == Brightness.dark;
   late final Color primaryColor = isDark ? Colors.grey[900]! : Colors.blue;
   final bool isScrollable;