localrepo: add "vfs" fields to "localrepository" for migration from "opener"
As a part of migration to vfs, this patch adds "vfs" fields to
"localrepository" class.
This allows new codes to access current "opener" objects related to
repositories via "vfs" fields, so patches referring to "vfs" will
replace referring to "opener" in time.
This patch also adds initializations for "vfs" fields to
"statichttprepository" class derived from it, because its constructor
doesn't invoke the constructor of "localrepository", so "vfs" fields
should be initialized explicitly as same as "opener" fields: it has no
working directory, so "wvfs" field is not added.