Optional parameters for TextClassifier APIs.

TextClassifier methods now take a @Nullable Options parameter which
is a container for optional parameters to its methods.
This way, if we need to pass an optional parameter to one of
TextClassifier's methods, we won't have to overload the method.
Instead, we'll introduce a new Options field.

This CL also adds a hidden optional field for suggestSelection.
This is used to make sure that "dark launched" models do not return
new selection indices to clients. Clients e.g. TextView that are
dark-launch aware may use the field to explicitly request for
dark-launch results.

Test: bit FrameworksCoreTests:android.widget.TextViewActivityTest
Test: bit CtsWidgetTestCases:android.widget.cts.TextViewTest
Test: Also see I843eadff8a2b674388055364c1f25c8d4ccea771
Change-Id: I58e44451ac8a8e3a5bc3959198447f5549870902