fix: conform replace outdated nested syntax

The syntax was changed in
stevearc/conform.nvim#491

The replacement for nested formatter is:
https://github.com/stevearc/conform.nvim/blob/master/doc/recipes.md#run-the-first-available-formatter-followed-by-more-formatters

lua/wangleng/plugins/lsp.lua

@@ -188,24 +188,45 @@ return {
     {
         'stevearc/conform.nvim',
         config = function()
-            -- second layer nesting is an either-or
-            -- e.g. formatter = { "eslint", { "prettierd", "prettier" }}
-            -- means: eslint AND (prettierd OR prettier)
-            local prettier = { "prettierd", "prettier" }
-            local eslint = "eslint_d"
-            local web_formatters = { eslint, prettier }
+            ---Selects the first available formatter.
+            ---
+            ---@param bufnr integer
+            ---@param ... string
+            ---@return string
+            local function first(bufnr, ...)
+                local conform = require("conform")
+                for i = 1, select("#", ...) do
+                    local formatter = select(i, ...)
+                    if conform.get_formatter_info(formatter, bufnr).available then
+                        return formatter
+                    end
+                end
+                return select(1, ...)
+            end
+
+            local function select_prettier(bufnr)
+                return first(bufnr, "prettierd", "prettier")
+            end
+
+            local function use_prettier(bufnr)
+                return { select_prettier(bufnr) }
+            end
+
+            local function use_web_formatters(bufnr)
+                return { "eslint_d", select_prettier(bufnr) }
+            end
 
             require("conform").setup({
                 formatters_by_ft = {
-                    javascript = web_formatters,
-                    javascriptreact = web_formatters,
-                    typescript = web_formatters,
-                    typescriptreact = web_formatters,
-                    html = { prettier },
-                    vue = web_formatters,
-                    svelte = web_formatters,
-                    json = { prettier },
-                    css = web_formatters,
+                    javascript = use_web_formatters,
+                    javascriptreact = use_web_formatters,
+                    typescript = use_web_formatters,
+                    typescriptreact = use_web_formatters,
+                    html = use_prettier,
+                    vue = use_web_formatters,
+                    svelte = use_web_formatters,
+                    json = use_prettier,
+                    css = use_web_formatters,
                 },
             })