pico_flash missing in pico_sdk

In the current pico_sdk, there are some helper functions for safely writing to flash in `pico_flash`:
https://github.com/raspberrypi/pico-sdk/blob/master/src/rp2_common/pico_flash/include/pico/flash.h

These are missing in
https://github.com/arduino/ArduinoCore-mbed/tree/main/cores/arduino/mbed/targets/TARGET_RASPBERRYPI/TARGET_RP2040/pico-sdk/rp2_common

I'm using both cores and `TBDStore` on `FlashIAPBlockDevice` on Arduino RP2040 nano connect. When storing values the controller stops. It works if I disable the second core. The functions in `pico_flash` simplify the lockout for such cases.

Start by reading pico-sdk/src/rp2_common/pico_flash/include/pico/flash.h, then compare its helper functions with the corresponding rp2_common tree under cores/arduino/mbed/targets/TARGET_RASPBERRYPI/TARGET_RP2040/pico-sdk. The work is done when the missing pico_flash helpers are available for Arduino RP2040 use and TBDStore on FlashIAPBlockDevice no longer stops the controller when both cores are enabled.

Written by the indexing model from the issue text.