Merge branch 'ps/setup-split-discovery-and-setup' into jch

The repository discovery and repository configuration phases, which
were previously intertwined in 'setup.c', have been split. Repository
discovery now populates a 'struct repo_discovery' without modifying
the repository state, and repository configuration takes this
structure to initialize the repository, paving the way for clean
unification of repository configuration.

* ps/setup-split-discovery-and-setup:
  setup: mark `set_git_work_tree()` as file-local
  setup: pass worktree to `init_db()`
  setup: drop redundant configuration of `startup_info->have_repository`
  setup: make repository discovery self-contained
  setup: propagate prefix via repository discovery
  setup: drop static `cwd` variable
  setup: move prefix into repository
  setup: embed repository format in discovery
  setup: introduce explicit repository discovery
  setup: split up concerns of `setup_git_env_internal()`
  setup: unify setup of shallow file
  setup: mark bogus worktree in `apply_repository_format()`
  setup: rename `check_repository_format_gently()`

diff --cc setup.c
Simple merge

diff --cc setup.h
Simple merge