Deduplicate cgroup code

[AustinWise]

It appears this code has been copy-pasted 4 times:

• src/coreclr/gc/unix/cgroup.cpp
• src/coreclr/nativeaot/Runtime/unix/cgroupcpu.cpp
• src/coreclr/pal/src/misc/cgroup.cpp
• src/mono/mono/utils/mono-cgroup.c

I'm guessing a good place to put a consolidated implementation is in src/native/minipal/.

There is also a fifth copy written in C# at src/libraries/Common/src/Interop/Linux/cgroups/Interop.cgroups.cs. I'm not sure if it is worthwhile to change the C# code to delegated to a common unmanaged implementation.

[jkotas]

cc @janvorli

[janvorli]

I'm guessing a good place to put a consolidated implementation is in src/native/minipal/.

Yes, we've already moved the utf8 code there from the coreclr PAL in the past.

I was actually not aware that mono used a clone of that code too. If there are any differences, I believe the files in src/coreclr/pal/src/misc/cgroup.cpp and src/coreclr/gc/unix/cgroup.cpp should be the source of truth.