Move lsp config to local file structure

.config/nvim/lsp/dartls.lua

@@ -0,0 +1,25 @@
+---@brief
+---
+--- https://github.com/dart-lang/sdk/tree/master/pkg/analysis_server/tool/lsp_spec
+---
+--- Language server for dart.
+
+---@type vim.lsp.Config
+return {
+  cmd = { 'dart', 'language-server', '--protocol=lsp' },
+  filetypes = { 'dart' },
+  root_markers = { 'pubspec.yaml' },
+  init_options = {
+    onlyAnalyzeProjectsWithOpenFiles = true,
+    suggestFromUnimportedLibraries = true,
+    closingLabels = true,
+    outline = true,
+    flutterOutline = true,
+  },
+  settings = {
+    dart = {
+      completeFunctionCalls = true,
+      showTodos = true,
+    },
+  },
+}