Add dartls

nvim/lua/lsp/servers/dartls.lua

@@ -0,0 +1,18 @@
+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,
+        },
+    },
+}