taskstats: export all kernel fields with names matching kernel names

[mdlayher]

Right now we export and rename an awkward subset of fields, but it's probably best to align more with what the kernel exports directly.

[gustavo-iniguez-goya]

This would be really useful for some applications @mdlayher . In particular, Ac_comm, Ac_uid, Ac_gid, Ac_exe_dev and Ac_exe_inode would be really interesting to have.

https://pkg.go.dev/golang.org/x/sys/unix#Taskstats