[vm/ffi] Pointer.asTypedList shared across isolates causes use after free

[dcharkes]

The native finalizers in asTypedList are bound to an isolate, not an isolate group:

sdk/sdk/lib/ffi/ffi.dart

Lines 368 to 373 in 4dd6ee6

	external Int8List asTypedList(
	int length, {
	@Since('3.1') Pointer<NativeFinalizerFunction>? finalizer,
	@Since('3.1') Pointer<Void>? token,
	});
	}

sdk/sdk/lib/_internal/vm/lib/ffi_native_finalizer_patch.dart

Line 115 in 4dd6ee6

final _asTypedListFinalizer = _NativeFinalizer(_asTypedListFinalizerCallback);

Hypothesis: The TypedData we create out of Pointer is marked unmodifiable.

We need to either mark the typed data as mutable so that the view does not consider the typed data as unmodifiable, and we copy instead of share the object.
Or, we need to attach finalizers in the isolate group instead of the isolate.

Context:

• JArray.getRange() has thread-safety problem native#1151

TODO: verify hypothesis. (Filing issue so that I don't forget.)