vfs: Add KASAN state transitions for vnodes

vnodes are a bit special in that they may exist on per-CPU lists even
while free. Add a KASAN-only destructor that poisons regions of each
vnode that are not expected to be accessed after a free.

Sponsored by: The FreeBSD Foundation

(cherry picked from commit b261bb4057f4abbc1366e4af8e9e4081d039be4a)