Similar to the create flow, make get request two staged.

Similar to the create flow, we will also split the get flow into the
candidate query stage (for displaying options) and the execution stage
(for getting a credential after a user makes the choice). This requires
the api to expose two request data getters: getCandidateQueryData for
the query stage and getRequestData for the execution stage.

Bug: 246564035
Bug: 253153445
CTS-Coverage-Bug: 246637346
Test: Local Build & Deployment
Change-Id: Ic63d8b257376beec039d8867e5b3ea1ab2d284e7