Renamed the GetCredentialOption to CredentialOptions.

GetCredentialOptions is an awkward name and leads to
getGetCredentialOptions() getter.

However, not moving it to be a subclass of ./GetCredentialRequest.java
because it's also used in service/credentials/GetCredentialRequest.java.

Test: CtsCredentialManagerTestCases
Bug: 265809787
CTS-Coverage-Bug: 263109618
API-Coverage-Bug: 263109618
Change-Id: I120735b37754bd8684e944c0cc89c826b402ef9f