Replace more literal strings with constants in libartbase/base/file_utils.cc.

Also use more uniform names for some of these constants as well.

Test: m test-art-host-gtest-file_utils_test
Bug: 129063331
Merged-In: I2bae31b242497d6e0275912c392b032ed1d623bb
Change-Id: I2bae31b242497d6e0275912c392b032ed1d623bb
(cherry picked from commit 9ff900dbb1ea9a617a73924104890aad868d265a)
2 files changed