Determine memory load based on cgroup usage. (dotnet/coreclr#19518)

Determine memory load based on cgroup usage. (dotnet/coreclr#19518)

cgroup usage is used to trigger oom kills. It includes rss and file cache
of the cgroup.

The implementation was only using the process rss to determine memory load.
This is less than the cgroup usage and leads to oom kills due to GC not
being triggered soon enough.

Commit migrated from https://github.com/dotnet/coreclr/commit/ca5b0d1caa47abdebac13233553c6e44db2e3168