i2c.c implements the legacy pyb.I2C class so rename the file to make this
explicit, and also to make room for an improved I2C driver.

By default the stm module is included in the build, but a board can now
define MICROPY_PY_STM to 0 to not include this module.  This reduces the
firmware by about 7k.

In particular don't issue a warning if the passed-in constraints are
actually supported because they are the default values.

Uses new pypi.org URL, and now creates a socket with the address parameters
returned by getaddrinfo().

To change the default label a board should define:

    #define MICROPY_HW_FLASH_FS_LABEL "label"

To use HSE bypass mode the board should define:

    #define MICROPY_HW_CLK_USE_BYPASS (1)

If this is not defined, or is defined to 0, then HSE oscillator mode is
used.

This patch allows a given board to configure which pins are used for the
CAN peripherals, in a similar way to all the other bus peripherals (I2C,
UART, SPI).  To enable CAN on a board the mpconfigboard.h file should
define (for example):

    #define MICROPY_HW_CAN1_TX (pin_B9)
    #define MICROPY_HW_CAN1_RX (pin_B8)
    #define MICROPY_HW_CAN2_TX (pin_B13)
    #define MICROPY_HW_CAN2_RX (pin_B12)

And the board config file should no longer define MICROPY_HW_ENABLE_CAN.

The individual union members (like SPI, I2C) are never used, only the
generic "reg" entry is.  And the union names can clash with macro
definitions in the HAL so better to remove them.

The only configuration that changes with this patch is that on L4 MCUs the
clock prescaler changed from ADC_CLOCK_ASYNC_DIV2 to ADC_CLOCK_ASYNC_DIV1
for the ADCAll object.  This should be ok.

A value of DISABLE for EOCSelection is invalid.  This would have been
interpreted instead as ADC_EOC_SEQ_CONV, but really it should be
ADC_EOC_SINGLE_CONV for the uses in this code.  So this has been fixed.

ExternalTrigConv should be ADC_SOFTWARE_START because all ADC
conversions are started by software.  This is now fixed.

Saves 200 bytes of code space.

This can be used to select the output buffer behaviour of the DAC.  The
default values are chosen to retain backwards compatibility with existing
behaviour.

Thanks to @peterhinch for the initial idea to add this feature.

Reading into a bytearray will truncate values to 0xff so the assertions
checking read_timed() would previously always succeed.

Thanks to @peterhinch for finding this problem and providing the solution.

This event queue has UART events posted to it and they need to be drained
for it to operate without error.  The queue is not used by the uPy UART
class so it should be removed to prevent the IDF emitting errors.

Fixes #3704.

Instead of emitnative.c having configuration code for each supported
architecture, and then compiling this file multiple times with different
macros defined, this patch adds a file per architecture with the necessary
code to configure the native emitter.  These files then #include the
emitnative.c file.

This simplifies emitnative.c (which is already very large), and simplifies
the build system because emitnative.c no longer needs special handling for
compilation and qstr extraction.

Keeping all the stress related tests in one place makes it easier to
stress-test a given port, and to also not run such tests on ports that
can't handle them.

Includes a fix for H7 DAC DMA requests.

This turns a hard crash in a recursive generator into a 'maximum recursion
depth exceeded' exception.

The 2nd and 3rd args of the ternary operator are treated like they are in
the same expression and must have similar types.  void is not compatible
with int so that's why the compiler is complaining.

This patch moves the implementation of stream closure from a dedicated
method to the ioctl of the stream protocol, for each type that implements
closing.  The benefits of this are:

1. Rounds out the stream ioctl function, which already includes flush,
   seek and poll (among other things).

2. Makes calling mp_stream_close() on an object slightly more efficient
   because it now no longer needs to lookup the close method and call it,
   rather it just delegates straight to the ioctl function (if it exists).

3. Reduces code size and allows future types that implement the stream
   protocol to be smaller because they don't need a dedicated close method.

Code size reduction is around 200 bytes smaller for x86 archs and around
30 bytes smaller for the bare-metal archs.