Create a utility function to copy a hostcode local buffer into the sandboxee. This combines the following steps into one API call:
1) Create a SAPI variable backed with the hostcode local buffer
2) Allocate the SAPI variable in the sandboxee's memory space
3) Transfer the SAPI variable into the sandboxee's memory space
The function returns a `std::unique_ptr` wrapped `sapi:✌️:RemotePtr` which points to the address of the buffer in the sandboxee's memory space.
PiperOrigin-RevId: 611151615
Change-Id: Ie5012bf17826614395d2056d560689fd9e429d75
86e356b7ee