Refactor art::GetAndroidDataSafe and art::GetAndroidData.

Make these methods return an `std::string` (instead of a
`const char*`), like similar methods of libartbase/base/file_utils.cc.

Test: m test-art-host-gtest-file_utils_test
Change-Id: Idf9ab45db3607d6079eaa8305e02b3483961f373
3 files changed