[NFC][TSan] Merge ScopedReportBase into ScopedReport (#228640) ScopedReport is the only subclass of ScopedReportBase and nothing uses ScopedReportBase directly. Merge ScopedReportBase into ScopedReport. Assisted-by: Gemini GitOrigin-RevId: e94b7487cf8ebe71744cd4137c9a0968affa0ec2