venv: recreate symlinks on --upgrade

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-03-16.13:57:10.325>
labels = ['type-feature', 'library']
title = 'venv: recreate symlinks on --upgrade'
updated_at = <Date 2021-08-27.05:46:23.840>
user = 'https://github.com/ThiefMaster'

bugs.python.org fields:

activity = <Date 2021-08-27.05:46:23.840>
actor = 'macpherson.scott'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2021-03-16.13:57:10.325>
creator = 'ThiefMaster'
dependencies = []
files = []
hgrepos = []
issue_num = 43513
keywords = []
message_count = 1.0
messages = ['388840']
nosy_count = 2.0
nosy_names = ['ThiefMaster', 'macpherson.scott']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue43513'
versions = []