Remove static fields in FfiNative's

[mkustermann]

Right now the FFI kernel transformer lowers @FfiNatives into static fields containing a lazily populated closure that is created by calling a resolution function.

Old natives do not require a static field, so this is in some ways a regression when switching from old natives to ffi natives.

We'd like to avoid usage of static fields for several reasons: It increases the root set in a way that scales as O(num-isolates x num-ffi-natives).

[dcharkes]

Not caching addresses in Dart fields would also enable us to think about supporting hot-reload for @FfiNatives when using:

• [vm/ffi] Native asset resolution by the Dart VM for FfiNatives #49803

Implementation pointer: https://dart-review.googlesource.com/c/sdk/+/264842/39/runtime/vm/isolate_reload.cc#2407