vts_libprocessgroup: Add vts_libprocessgroup

Test kernel UAPI surrounding memory control groups version 2. These are
not accessible to normal apps but can be used by Android native
libraries in some configurations.

Bug: 331795334
Bug: 384285412
Test: atest vts_libprocessgroup (with and without -extra_kernel_cmdline cgroup_disable=memory)
Change-Id: Ic08649f3d39bbce0fd93da1767250a88f2501ef9