Properly report intrinsic fields (dotnet/corertdotnet/coreclr#6602)

Properly report intrinsic fields (dotnet/corertdotnet/coreclr#6602)

* Properly report intrinsic fields

We were hitting an assert in RyuJIT because we were reporting IntPtr.Zero as an intrinsic even if we were not trying to `CORINFO_ACCESS_GET`.

I fixed that part and also went ahead to port the rest of getFieldIntrinsic from CoreCLR. We'll need this anyway.

* Add intrinsic fields

Signed-off-by: dotnet-bot <dotnet-bot@microsoft.com>
Commit migrated from https://github.com/dotnet/coreclr/commit/e6e582cfca205692ef4e0cb9300abc6c9abab9e6