Fix flag value for configuration_optional widget feature.

The flag value should be 4 and not 3 so that we can use bitwise
operations to determine the existence of a flag.

For example, we want to use the following to determine if a widget is
reconfigurable:
(providerInfo.widgetFeatures & WIDGET_FEATURE_RECONFIGURABLE) != 0
But if the value of WIDGET_FEATURE_CONFIGURATION_OPTIONAL is 3, the
above check would fail.

Test: atest FrameworksServicesTests:AppWidgetServiceImplTest, atest
CtsAppWidgetTestCases
Bug: 177977976

Change-Id: I15d4baae5e17acb9a0b936485a53f9b3359d65ca