Configure stylua to collapse simple inline lua functions

This config prevents stylua from changing one-liners like this:
vim.keymap.set('n', '<C-j>', function() harpoon:list():select(1) end)

to this:
vim.keymap.set('n', '<C-j>', function()
  harpoon:list():select(1)
end)

.stylua.toml

@@ -4,3 +4,4 @@ indent_type = "Spaces"
 indent_width = 2
 quote_style = "AutoPreferSingle"
 call_parentheses = "None"
+collapse_simple_statement = "FunctionOnly"