Expose ServiceSpecificException as @SystemApi.

This class is useful as a system API because:

- It is one of the few exceptions that is natively Parcelable.
- It is directly supported by native code without using JNI,
  using Status::fromServiceSpecificError.
- Unlike other natively parcelable exceptions, it contains both
  an error message and an error code.

Test: m
Bug: 112869080
Change-Id: Ica3e88c2b6877e429a61b053d75f69b9f19fc74a