Use custom action key icon

1. get icon from getKeyboardSettingsFeatureProvider
2. set color for it

Bug: 269214138
Test: manual, atest KeyboardSettingsFeatureProviderImplTest
Change-Id: I3a2d47e8230aec1404300b000e8b1fcf221e2a65

tests/unit/src/com/android/settings/inputmethod/KeyboardSettingsFeatureProviderImplTest.java

@@ -57,4 +57,9 @@ public class KeyboardSettingsFeatureProviderImplTest {
 
         assertThat(mFeatureProvider.addFirmwareUpdateCategory(mContext, screen)).isFalse();
     }
+
+    @Test
+    public void getActionKeyIcon_defaultValue_returnsNull() {
+        assertThat(mFeatureProvider.getActionKeyIcon(mContext)).isNull();
+    }
 }