Expand concurrent.futures.Future's public API

GitHub fields:

assignee = 'https://github.com/aeros'
closed_at = None
created_at = <Date 2020-02-16.07:38:05.012>
labels = ['type-feature', 'library', '3.9']
title = "Expand concurrent.futures.Future's public API"
updated_at = <Date 2020-06-12.21:00:12.550>
user = 'https://github.com/aeros'

bugs.python.org fields:

activity = <Date 2020-06-12.21:00:12.550>
actor = 'jakirkham'
assignee = 'aeros'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2020-02-16.07:38:05.012>
creator = 'aeros'
dependencies = []
files = []
hgrepos = []
issue_num = 39645
keywords = []
message_count = 10.0
messages = ['362047', '362110', '362163', '363114', '363117', '363119', '363121', '363124', '363205', '368440']
nosy_count = 7.0
nosy_names = ['gvanrossum', 'bquinlan', 'pitrou', 'Big Stone', 'aeros', 'iforapsy', 'jakirkham']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue39645'
versions = ['Python 3.9']