Monotonic time on macOS 10.12+ should use mach_continuous_time()

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-10-21.10:37:25.123>
labels = ['OS-mac', 'type-bug', '3.10']
title = 'Monotonic time on macOS 10.12+ should use mach_continuous_time()'
updated_at = <Date 2020-10-21.18:55:54.519>
user = 'https://github.com/xsetech'

bugs.python.org fields:

activity = <Date 2020-10-21.18:55:54.519>
actor = 'ronaldoussoren'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['macOS']
creation = <Date 2020-10-21.10:37:25.123>
creator = 'sjunot'
dependencies = []
files = []
hgrepos = []
issue_num = 42107
keywords = []
message_count = 2.0
messages = ['379204', '379231']
nosy_count = 4.0
nosy_names = ['ronaldoussoren', 'vstinner', 'ned.deily', 'sjunot']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue42107'
versions = ['Python 3.10']