rust: Support sanitizers in rust_ffi modules

Don't automatically assume that HWASAN or ASAN is enabled if Fuzzer is
enabled.

Bug: 178365482
Test: m bluetooth_stack_with_facade
Test: SANITIZE_TARGET=fuzzer m bluetooth_stack_with_facade
Test: SANITIZE_TARGET=address m bluetooth_stack_with_facade
Test: SANITIZE_TARGET=hwaddress m bluetooth_stack_with_facade
Test: SANITIZE_TARGET="fuzzer address" m bluetooth_stack_with_facade
Test: SANITIZE_TARGET="fuzzer hwaddress" m bluetooth_stack_with_facade
Change-Id: Ief8c0f899837c5889a8035782616025f1b0d54e7