setup: stop using `the_repository` in `setup_work_tree()`

setup: stop using `the_repository` in `setup_work_tree()`

Stop using `the_repository` in `setup_work_tree()` and instead accept
the repository as a parameter. The injection of `the_repository` is thus
bumped one level higher, where callers now pass it in explicitly.

Note that the function tracks two bits of information via global
variables. This of course doesn't make much sense anymore now that we
can set up worktrees for arbitrary repositories:

  - We track whether the worktree has already been initialized and, if
    so, we skip the call to `chdir_notify()` and setenv(3p). It does not
    make much sense to store this info in the repository, as we _would_
    want to update the environment when switching between worktrees back
    and forth.

    So instead of storing this info in the repository, we drop this
    state entirely and live with the fact that we may execute the logic
    twice. It should ultimately be idempotent though and thus not be
    much of a problem.

  - We track whether the worktree configuration is bogus. If so, and if
    later on some caller tries to setup the worktree, then we'll die
    instead. This is indeed information that we can move into the
    repository itself.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>