Currently the stack limit margin is hard-coded in each port's call to
`mp_stack_set_limit()`, but on threaded ports it's fiddlier and can lead to
bugs (such as incorrect thread stack margin on esp32).
This commit provides a new API to initialise the C Stack in one function
call, with a config macro to set the margin. Where possible the new call
is inlined to reduce code size in thread-free ports.
Intended replacement for `MP_TASK_STACK_LIMIT_MARGIN` on esp32.
The previous `stackctrl.h` API is still present and unmodified apart from a
deprecation comment. However it's not available when the
`MICROPY_PREVIEW_VERSION_2` macro is set.
This work was funded through GitHub Sponsors.
Signed-off-by: Angus Gratton <angus@redyak.com.au>
