InstanceIdentifierBuilder needs to be a copy-based builder

The default InstanceIdentifierBuilder needs to be a copy builder, such that it has stable state and the following code is valid (seen in the wild):

InstanceIdentifierBuilder<Foo> foob = InstanceIdentfier.builder(Foo.class);

dataProviderService.removeOperationalData(foob.augmentation(Bar.class).build));
dataProviderService.removeOperationalData(foob.augmentation(Baz.class).build));

Once it is stable, also add hashCode()/equals() so it can be kept around safely.

The current mutable version may be retained as an explicit MutableInstanceIdentifierBuilder or something of that kind.