Optimize calling pure python descriptor __get__ with vectorcall

[kumaraditya303]

Benchmark:

import pyperf
from pyperf import Runner


class Descr:

    def __init__(self, value):
        self.value = value

    def __get__(self, instance, owner):
        return self.value


class A:
    x = Descr(1)


def bench(loops):
    a = A()
    t1 = pyperf.perf_counter()
    for _ in range(loops):
        a.x
    t2 = pyperf.perf_counter()
    return t2 - t1


runner = Runner()
runner.bench_time_func('descriptor', bench)

Results:

@kumaraditya303 ➜ /workspaces/cpython (main ✗) $ ./python -m pyperf compare_to base.json patch.json 
Mean +- std dev: [base] 102 ns +- 6 ns -> [patch] 88.5 ns +- 4.0 ns: 1.15x faster