virtualenv: Bash activator leaves the --prompt value unescaped in PS1 when promptvars is off, so prompt expansion later executes it (regression in 21.14.9)

Summary The bash activator puts the caller-supplied prompt value into PS1 unescaped whenever promptvars is off at activation time, and assumes prompt expansion can never run afterwards. promptvars and posix mode are runtime shell state, not a property of the activation moment: re-enabling prompt...