Closure::ToCString allocates heap memory which upsets vm/cc/ToCString test #61716
Description
Closure::ToCString calls Closure::GetInstantiatedSignature which calls FunctionType::InstantiateFrom which needs to allocate instantiated type.
We probably should split Closure::ToCString into safe and unsafe version.
This was revealed by my changes in https://dart-review.googlesource.com/c/sdk/+/454062?tab=checks