[Angel] Add skeleton SafetyPreferenceData and SafetyIssueData classes

* This adds some trivial fields in SafetyPreferenceData and SafetyIssueData.
* Structure and naming is being discussed in go/angel-safetysourcedata
* Fields of type SafetyPreferenceData and SafetyIssueData will be added to SafetySourceData

Test: Will add CTS tests when API is moved to `framework-s`.
Bug: 203506135
Change-Id: I7f04dae2ee9786c00a7e5f2290f5192660f1718b