[RFC PATCH 1/4] ls-tree: don't use "show_tree_data" for "fast" callbacks

> As noted in [1] the code that made it in as part of
> 9c4d58ff2c3 (ls-tree: split up "fast path" callbacks, 2022-03-23) was
> a "maybe a good idea, maybe not" RFC-quality patch. I hadn't looked
> very carefully at the resulting patterns.
>
> The implementation shared the "struct show_tree_data data", which was
> introduced in e81517155e0 (ls-tree: introduce struct "show_tree_data",
> 2022-03-23) both for use in 455923e0a15 (ls-tree: introduce "--format"
> option, 2022-03-23), and because the "fat" callback hadn't been split
> up as 9c4d58ff2c3 did.
>
> Now that that's been done we can see that most of what
> show_tree_common() was doing could be done lazily by the callbacks
> themselves, who in the pre-image were often using an odd mis-match of
> their own arguments and those same arguments stuck into the "data"
> structure. Let's also have the callers initialize the "type", rather
> than grabbing it from the "data" structure afterwards.
>
> 1. https://lore.kernel.org/git/cover-0.7-00000000000-20220310T134811Z-avarab@gmail.com/