Introduce FakeContextBuilder

This helps us build a fake context where we can configure things like
what activity can handle an intent or whether no activity can handle
an intent.
The hope is that we can fake several aspects of the context used for
testing here. If our configuration requirements become too complex
in the future, we should probably consider creating more focused
fake context builders.

The immediate use case for this builder is for configuring what actions
are returned by the text classifier as activities that can handle a
specified text classifier query.

Test: atest android.view.textclassifier.TextClassificationManagerTest
Bug: 34780395
Change-Id: Ifd3d6cff928cc2f11b69206660b6d7c4791f1c0f