This is discuseed in Using esp-idf library within the Arduino Framework (ESP32).
For your specific case: The Bluetooth hands-free profile audio gateway APIs, as seen in here, while the header file is included in the latest Arduino-ESP32, see e.g. here, it is not actually usuable because the component was deactivated on compile-time.
If that was not the case you would have been able to call into these ESP-IDF APIs from within just a pure Arduino-ESP32 environment.
So you’ll have to resort to the ESP-IDF plus Arduino as a component method for this one.
Note that currently there’s a caveat in the PlatformIO-provided example: espidf-arduino-blink example uncompilable because of missing branch · Issue #524 · platformio/platform-espressif32 · GitHub.