genfs_contexts

New types and files labeled with them:
1. proc_abi:
  /proc/sys/abi/swp

2. proc_dirty:
  /proc/sys/vm/dirty_background_ratio
  /proc/sys/vm/dirty_expire_centisecs

3. proc_diskstats:
  /proc/diskstats

4. proc_extra_free_kbytes:
  /proc/sys/vm/extra_free_kbytes

5. proc_hostname:
  /proc/sys/kernel/domainname
  /proc/sys/kernel/hostname

6. proc_hung_task:
  /proc/sys/kernel/hung_task_timeout_secs

7. proc_max_map_count:
  /proc/sys/vm/max_map_count

8. proc_panic:
  /proc/sys/kernel/panic_on_oops

9. proc_sched:
  /proc/sys/kernel/sched_child_runs_first
  /proc/sys/kernel/sched_latency_ns
  /proc/sys/kernel/sched_rt_period_us
  /proc/sys/kernel/sched_rt_runtime_us
  /proc/sys/kernel/sched_tunable_scaling
  /proc/sys/kernel/sched_wakeup_granularity_ns

10. proc_uptime:
  /proc/uptime

Files labeled with already existing types:
1. proc_perf:
  /proc/sys/kernel/perf_event_paranoid

2. proc_sysrq:
  /proc/sys/kernel/sysrq

3. usermodehelper:
  /proc/sys/kernel/core_pipe_limit

Changes to init domain:
1. Removed access to files with 'proc' label.
2. Added access to newly introduced types + proc_kmsg.

Bug: 68949041
Test: walleye boots without denials from u:r:init:s0.
Test: system/core/init/grab-bootchart.sh does not trigger denials from
u:r:init:s0
Change-Id: If1715c3821e277679c320956df33dd273e750ea2