Add/merge port/board specific sections (pins) into machine.pyi

[Josverl]

Example : the rp2 machine.pyi
https://github.com/paulober/Pico-W-Stub/blob/main/frozen/umachine.pyi
possibly based on ports/<port>/boards<board>/pins.csv ? for each board

• Use Pin Class for GP.* / EXT_GP.* members
• update init signature
• add comments based on Pins

    class cpu:
        GPIO20: Incomplete
        GPIO25: Incomplete
        GPIO26: Incomplete

    class board:
        GP3: Incomplete
        GP28: Incomplete
        GP4: Incomplete
        GP5: Incomplete

to

    class board():
        GP0 : Pin
        """ <class 'Pin'> = Pin(GPIO0, mode=ALT, pull=PULL_DOWN, alt=31) """
        GP1 : Pin
        """ <class 'Pin'> = Pin(GPIO1, mode=ALT, pull=PULL_DOWN, alt=31) """


    class cpu():

        EXT_GPIO0 : Pin
        """ <class 'Pin'> = Pin(EXT_GPIO0, mode=IN) """
        EXT_GPIO1 : Pin
        """ <class 'Pin'> = Pin(EXT_GPIO1, mode=IN) """
        EXT_GPIO2 : Pin
        """ <class 'Pin'> = Pin(EXT_GPIO2, mode=IN) """
        GPIO0 : Pin
        """ <class 'Pin'> = Pin(GPIO0, mode=ALT, pull=PULL_DOWN, alt=31) """