Fixing issue for identical surfaces in shared mode

The Camera2 Multi-Client API failed when an application requested
multiple streams with identical configurations (e.g., same resolution
and format).

The root cause was that the same stream ID was assigned to each
identical stream configuration based on the `shared_session_config.xml`.
This resulted in the configuration for one stream being overwritten by
another in the client's map of configured outputs. Consequently, when
`setRepeatingRequest` was called, the system threw an
`IllegalArgumentException` due to an "unconfigured Input/Output
Surface".

This change updates the stream ID assignment logic to ensure that each
requested stream surface receives a unique, unused stream ID from the
pool of available streams defined in the shared configuration. This
allows clients to successfully open and operate multiple identical
streams concurrently in a shared camera session.

To support N identical streams, the shared session configuration XML
must contain N corresponding `<OutputConfiguration>` entries.

Flag: EXEMPT BUGFIX
Bug: 437799042
Test: Run CTS SharedCameraTest
Change-Id: Ia704efe9392518234ef740579ab663fc628b2654