feat: support tables as keys in setup({ formatters_by_ft })

[drowning-cat]

require('conform').setup({
  -- You can use tables as keys to define multiple file types for the same formatter config
  [{ "bash", "csh", "ksh", "sh", "zsh" }] = { "beautysh" },
  -- Simple keys always override tables as keys, regardless of order
  bash = { "shfmt" },
})

There is only one caveat: lua-language-server currently does not support type annotations for table keys.
See LuaLS/lua-language-server#2610 for more details.

[stevearc]

I appreciate the work that went into this, but I'm not interested in adding this syntax to setup. I have intentionally tried to make the interface as simple and stupid as possible, I've actually removed some old features because they complicated the API. It's easier to learn, easier to read, and is a hard guard against scope creep. I've had issues with my other plugins where feature request upon feature request causes the config options to explode. My current stance is that if it's something that can reasonably be done in the end-user config, it should be. Given that this is just a small bit of syntactic sugar to save a few lines, I don't think it's worth adding.