Don't assume objects don't escape in pure helpers.

Don't assume objects don't escape in pure helpers.

We can't assume objects don't escape in helpers marked as pure for the following reasons:

1. The helpers may call user code that may make objects escape, e.g.,
https://github.com/dotnet/coreclr/blob/dotnet/coreclr@c94d8e68222d931d4bb1c4eb9a52b4b056e85f12/src/vm/jithelpers.cpp#L2371

2. The helpers usually protect gc pointers with GCPROTECT_BEGIN() so the pointers are reported as normal pointers to the gc.
Pointers to stack-allocated objects need to be reported as interior so they have to be protected with
GCPROTECT_BEGININTERIOR().

3. The helpers may cause these asserts in ValidateInner on stack-allocated objects:
https://github.com/dotnet/coreclr/blob/dotnet/coreclr@c94d8e68222d931d4bb1c4eb9a52b4b056e85f12/src/vm/object.cpp#L723
https://github.com/dotnet/coreclr/blob/dotnet/coreclr@c94d8e68222d931d4bb1c4eb9a52b4b056e85f12/src/vm/object.cpp#L730

Commit migrated from https://github.com/dotnet/coreclr/commit/65f88672f888e893a44f21b59ecfd87f4d17e499