Auto-generate the stmhal/pybcdc_inf header file from static files

The USB VID&PID are automatically extracted from usbd_desc_cdc_msc.c
and inserted into pybcdc_inf.template, ensuring that the same USB
IDs get used everywhere

As discussed [here](https://github.com/micropython/micropython/commit/b99ca2cdde4e728308152028db9e67f2c33dde8f#commitcomment-5993628)