vim.iter: flatten() non-list input

[justinmk]

Problem

iter:flatten() currently fails ("flatten() requires a list-like table") on this code from gen_lsp.lua:

neovim/scripts/gen_lsp.lua

Lines 262 to 265 in 35e3883

	local anonym = vim.tbl_flatten { -- remove nil
	anonymous_num > 1 and '' or nil,
	'---@class ' .. anonymous_classname,
	}

local anonym = vim.iter({ -- remove nil
  anonymous_num > 1 and '' or nil,
  '---@class ' .. anonymous_classname,
}):flatten():totable()

Expected behavior

tbl_flatten accepted array-like input and the above gen_lsp code leveraged that to drop nil items.

Can we enhance Iter:flatten() to work for arrays?

[clason]

Duplicate of #28777 (which has more information and will be closed by #28781)