Ensure self-managed CS can use any URI scheme.

There was previously an assumption that only SIP or TEL calls could
be placed.  Removed this dependency for self-managed CS and added
TODOs so we know to clean up this assumption in the future.

Also added small fix to unit tests for existing breakage.

Test: Added CTS test coverage, ran unit tests, manual test.
Bug: 77581565
Change-Id: I812260bd1aab560503e833ad60f8daaf80d5dd90