When using esp-idf, files embedding process works little different that current docs suggest

See https://docs.platformio.org/en/latest/platforms/espressif32.html#embedding-binary-data (sources at https://github.com/platformio/platformio-docs/blob/develop/frameworks/espidf_extra.rst).

The docs suggest using _binary_src_ prefix (to compensate for src/ folder) in externs for the embedded data labels. Meanwhile (at least for me) generated files and labels do not include the src_ prefix, just _binary_ alone.

The solution might need some refining (and confirmation) I guess. I am not confident with PlatformIO / esp-idf myself, but I am posting it here (as an issue) so maybe other, more knowledgeable people could look at it. Anyway, it works for me ;)

Start with frameworks/espidf_extra.rst and the embedded binary data section at the linked documentation URL. Reproduce the ESP-IDF embedding flow and compare the generated files and labels with the documented extern prefix. Done means the documentation accurately reflects the observed naming or clearly explains the conditions where it differs.