Add elevation to Chips to allow for more flexibility (#27316)

Expose elevation on chips and allow for it to be customized by the developer.

packages/flutter/test/material/chip_test.dart

@@ -1484,7 +1484,7 @@ void main() {
 
     final ChipThemeData chipTheme = theme.chipTheme;
 
-    InputChip inputChip = const InputChip(label: Text('Label'), pressElevation: 8.0);
+    InputChip inputChip = const InputChip(label: Text('Label'));
 
     Widget buildChip(ChipThemeData data) {
       return _wrapForChip(
@@ -1498,12 +1498,18 @@ void main() {
 
     await tester.pumpWidget(buildChip(chipTheme));
     expect(inputChip.pressElevation, 8.0);
+    expect(inputChip.elevation, 0.0);
 
-    inputChip = const InputChip(label: Text('Label'), pressElevation: 12.0);
+    inputChip = const InputChip(
+      label: Text('Label'),
+      pressElevation: 12.0,
+      elevation: 4.0,
+    );
 
     await tester.pumpWidget(buildChip(chipTheme));
     await tester.pumpAndSettle();
     expect(inputChip.pressElevation, 12.0);
+    expect(inputChip.elevation, 4.0);
   });
 
   testWidgets('can be tapped outside of chip body', (WidgetTester tester) async {