Add fixupAppDir() API.

This can be used to fixup application directories in case they have been
created by some other entity besides vold; the main use case for this
API right now is OBB directories, which can be created by installers
outside of vold; on devices without sdcardfs, such directories and the
files contained therein are not setup correctly. This API will make sure
everything is setup the way it needs to be setup.

Bug: 146419093
Test: inspect OBB dir after install
Change-Id: I2e35b7ac2992dbb21cc950e53651ffc07cfca907
diff --git a/Android.bp b/Android.bp
index a420078..676c958 100644
--- a/Android.bp
+++ b/Android.bp
@@ -167,6 +167,7 @@
     ],
     whole_static_libs: [
         "com.android.sysprop.apex",
+        "libc++fs"
     ],
 }