native shared libs in an SDK can be snapshotted

The snapshot script can now handle native shared libs in an SDK.

Bug: 138182343
Test: create following sdk module:
sdk {
    name: "mysdk",
    native_shared_libs: ["libc", "libdl"],
}
, then execute `m mysdk` and execute the update_prebuilt-1.sh as
prompted. Following directories are generated under the directory where
mysdk is defined at:

1
├── aidl
├── Android.bp
├── arm64
│   ├── include
│   ├── include_gen
│   └── lib
│       ├── libc.so
│       └── libdl.so
├── include
│   └── bionic
│       └── libc
│           └── include
│               ├── alloca.h
│               ├── android
│               │   ├── api-level.h
<omitted>

Change-Id: Ia1dcc5564c1cd17c6ccf441d06d5995af55db9ee