Rust API to fuzz multiple binders

Adding rust wrapper fuzz_multiple_services so that multiple binders can be fuzzed together.

Test: m keystore_service_fuzzer && adb sync data && adb shell
/data/fuzz/$(get_build_var
TARGET_ARCH)/keystore_service_fuzzer/keystore_service_fuzzer -runs=1000
Bug: 296464642

Change-Id: I2392141a53fbf38aba84074ab6f6e14574a151fa