[nrf fromtree] storage/stream_flash: Add API to query buffered data size#3247

rlubos merged 2 commits intonrfconnect:mainnrfconnect/sdk-zephyr:mainfrom

SyverHaraldsen:FOTA_resumption_fixSyverHaraldsen/sdk-zephyr:FOTA_resumption_fixCopy head branch name to clipboard