Simplify (and fix) refcounts in createAt.
Simplify (and fix) refcounts in createAt.

fileOpAt holds references on the Dirents passed as arguments to the callback,
and drops refs when finished, so we don't need to DecRef those Dirents
ourselves

However, all Dirents that we get from FindInode/FindLink must be DecRef'd.

This CL cleans up the ref-counting logic, and fixes some refcount issues in the
process.

PiperOrigin-RevId: 256220882

google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor