rust: Use rust_ffi for Rust generated C libraries.

We no longer have the rust_library_shared and rust_library_static module
types. They've been renamed to rust_ffi_* instead. This brings
cargo2android.py up to date.

Bug: 175155132
Test: cargo2android's Android.bp for libquiche contains rust_ffi modules
Change-Id: I01bb8b4e56c41d36481ffd363f96aecb770d7cb8
1 file changed