Merge remote-tracking branch 'aosp/upstream' into master

* aosp/upstream:
  Add pathtools.Filesystem.Stat for soong_zip
  Add tests for pathtools.FileSystem.Lstat
  Add pathtools.FileSystem.Readlink
  Replace exact errors in tests with errno checking
  Make pathtools.FileSystem.Open return a ReaderAtSeekerCloser
  Fix typo in TestMockFs_followSymlinks

Bug: 116751500
Test: fs_test.go
Test: m checkbuild
Change-Id: Idc1d0a5c87f6c7b48f6b73106620c9a36e4259e2