ASharedMemory C++ wrapper API

Forked from https://github.com/android-ndk/ndk/issues/476

Possible API:

```C++
namespace android::memory {
class SharedMemory final {
public:
SharedMemory (const std::string& name, size_t size);
SharedMemory (std::string_view name, size_t size);
~SharedMemory(); // Use RAII to release the memory

size_t getSize ();
int setProt (int prot)
};
}
```

The issue names no files, tests, or implementation entry point. Start by reading the forked android-ndk/ndk#476 discussion and reviewing the existing NDK shared-memory APIs; clarify the supported API surface and acceptance criteria before coding.

Written by the indexing model from the issue text.