add FileInput.rollback() for in-place filters

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-08-10.22:22:25.243>
labels = ['type-feature', 'library', '3.9', '3.10', '3.11']
title = 'add FileInput.rollback() for in-place filters'
updated_at = <Date 2021-08-10.22:29:22.249>
user = 'https://bugs.python.org/samwyse'

bugs.python.org fields:

activity = <Date 2021-08-10.22:29:22.249>
actor = 'samwyse'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2021-08-10.22:22:25.243>
creator = 'samwyse'
dependencies = []
files = []
hgrepos = []
issue_num = 44882
keywords = []
message_count = 1.0
messages = ['399361']
nosy_count = 1.0
nosy_names = ['samwyse']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue44882'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']