* bpo-37986: Improve perfomance of PyLong_FromDouble()

* Use strict bound check for safety and symmetry

* Remove possibly outdated performance claims

Co-authored-by: Mark Dickinson <dickinsm@gmail.com>

* bpo-40455: Remove gcc10 warning about x_digits

* bpo-40455: nit

* bpo-40455: fix logic error

pycore_pystate.h no longer includes pycore_interp.h:
it's now included explicitly in files accessing PyInterpreterState.

The bulk of this patch was generated automatically with:

    for name in \
        PyObject_Vectorcall \
        Py_TPFLAGS_HAVE_VECTORCALL \
        PyObject_VectorcallMethod \
        PyVectorcall_Function \
        PyObject_CallOneArg \
        PyObject_CallMethodNoArgs \
        PyObject_CallMethodOneArg \
    ;
    do
        echo $name
        git grep -lwz _$name | xargs -0 sed -i "s/\b_$name\b/$name/g"
    done

    old=_PyObject_FastCallDict
    new=PyObject_VectorcallDict
    git grep -lwz $old | xargs -0 sed -i "s/\b$old\b/$new/g"

and then cleaned up:

- Revert changes to in docs & news
- Revert changes to backcompat defines in headers
- Nudge misaligned comments

Replace direct acccess to PyVarObject.ob_size with usage of
the Py_SET_SIZE() function.

Replace direct access to PyObject.ob_type with Py_TYPE().

Remove:

* COUNT_ALLOCS macro
* sys.getcounts() function
* SHOW_ALLOC_COUNT code in listobject.c
* SHOW_TRACK_COUNT code in tupleobject.c
* PyConfig.show_alloc_count field
* -X showalloccount command line option
* @test.support.requires_type_collecting decorator

Add _Py_bit_length() to unify duplicate bits_in_digit() and bit_length().