[Material] FAB refactor - remove unnecessary IconTheme (#37269)

* Remove unneeded IconTheme from FAB

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

@@ -431,18 +431,7 @@ class FloatingActionButton extends StatelessWidget {
       ?? floatingActionButtonTheme.shape
       ?? (isExtended ? _defaultExtendedShape : _defaultShape);
 
-    Widget result;
-
-    if (child != null) {
-      result = IconTheme.merge(
-        data: IconThemeData(
-          color: foregroundColor,
-        ),
-        child: child,
-      );
-    }
-
-    result = RawMaterialButton(
+    Widget result = RawMaterialButton(
       onPressed: onPressed,
       elevation: elevation,
       focusElevation: focusElevation,
@@ -458,7 +447,7 @@ class FloatingActionButton extends StatelessWidget {
       shape: shape,
       clipBehavior: clipBehavior ?? Clip.none,
       focusNode: focusNode,
-      child: result,
+      child: child,
     );
 
     if (tooltip != null) {

packages/flutter/test/material/floating_action_button_test.dart

@@ -781,6 +781,23 @@ void main() {
       ),
     );
   }, semanticsEnabled: true);
+
+  testWidgets('Foreground color applies to icon on fab', (WidgetTester tester) async {
+    const Color foregroundColor = Color(0xcafefeed);
+
+    await tester.pumpWidget(MaterialApp(
+      home: FloatingActionButton(
+        onPressed: () {},
+        foregroundColor: foregroundColor,
+        child: const Icon(Icons.access_alarm),
+      ),
+    ));
+
+    final RichText iconRichText = tester.widget<RichText>(
+      find.descendant(of: find.byIcon(Icons.access_alarm), matching: find.byType(RichText)),
+    );
+    expect(iconRichText.text.style.color, foregroundColor);
+  });
 }
 
 Offset _rightEdgeOfFab(WidgetTester tester) {