Use mapped device number + topmost inode number for all files in VFS2 overlay.

Before this CL, VFS2's overlayfs uses a single private device number and an
autoincrementing generated inode number for directories; this is consistent
with Linux's overlayfs in the non-samefs non-xino case. However, this breaks
some applications more consistently than on Linux due to more aggressive
caching of Linux overlayfs dentries.

Switch from using mapped device numbers + the topmost layer's inode number for
just non-copied-up non-directory files, to doing so for all files. This still
allows directory dev/ino numbers to change across copy-up, but otherwise keeps
them consistent.

Fixes #5545:
```
$ docker run --runtime=runsc-vfs2-overlay --rm ubuntu:focal bash -c "mkdir -p 1/2/3/4/5/6/7/8 && rm -rf 1 && echo done"
done
```

PiperOrigin-RevId: 359350716

0 files changed, 0 insertions, 0 deletions