py/persistentcode: Make .mpy files a bit more compact with qstr directly in prelude.

[dpgeorge]

Instead of encoding 4 zero bytes as placeholders for the simple_name and source_file qstrs, and storing the qstrs after the bytecode, store the qstrs at the location of these 4 bytes.

This will reduce .mpy files byte 4 bytes for each function in them. Eg lcd160cr.mpy drops by 232 bytes (4* 58 functions).

Code size change is:

   bare-arm:    +0 +0.000%
minimal x86:    +0 +0.000%
   unix x64:  -120 -0.024%
unix nanbox:   -64 -0.014%
      stm32:   -60 -0.017% PYBV10
     cc3200:   -32 -0.017%
    esp8266:   -52 -0.008%
      esp32:   +12 +0.001% GENERIC
        nrf:    +0 +0.000% pca10040
       samd:    +0 +0.000% ADAFRUIT_ITSYBITSY_M4_EXPRESS