Add getBackportedFixStatus to android.os.Build

This is a public API app developers use to check if a known issue is fixed
on a device.

Flag: android.os.api_for_backported_fixes
Bug: 308461809
Test: atest CtsOsTestCases:android.os.cts.BuildTest CtsOsTestCases:android.os.cts.CriticalIssuesTest
Change-Id: Ic0dea51d1b5b1746b55f76e0e39d2fca8f73ee70
2 files changed