Re: [PATCH v2 6/8] checkout: restructure switch, restore, and checkout entrypoints

cmd_switch(), cmd_restore(), and cmd_checkout() pass their options
to checkout_main(), which parses options and configuration,
validates and dispatches to checkout_branch() or checkout_paths().

Now that option initialization, validation, and branch setup have been
split into dedicated helper functions, restructure cmd_switch(),
cmd_restore(), and cmd_checkout() to invoke these helpers directly and
dispatch to checkout_branch() or checkout_paths().

In cmd_restore(), handle the --staged default from_treeish = "HEAD" and
resolve opts.from_treeish into new_branch_info and opts.source_tree.

This allows us to remove checkout_main() and enum checkout_command
as they are no longer needed.

Signed-off-by: Junio C Hamano <redacted>
---
 builtin/checkout.c | 297 +++++++++++++++++++++++----------------------
 1 file changed, 149 insertions(+), 148 deletions(-)

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 2edaca5539..b18515ac7f 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c

@@ -1341,12 +1341,6 @@ static void setup_new_branch_info_and_source_tree(
 }


-enum checkout_command {
-	CHECKOUT_CHECKOUT = 1,
-	CHECKOUT_SWITCH = 2,
-	CHECKOUT_RESTORE = 3,
-};
-