Switch the parse tree tests to lit (#2289)

This switch is being done in order to make it easier to update tests when the parse tree structure changes. I've been spending a lot of time doing such updates as part of refactoring the parse tree, and I expect more, so that's really at the root of all the refactoring I've been doing to lit updates.

toolchain/parser/testdata/function/declaration/basic.carbon

@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// RUN: %{carbon} dump parse-tree %s | %{FileCheck-strict} %s
+// AUTOUPDATE: %{carbon} dump parse-tree %s
+// CHECK:STDOUT: [
+// CHECK:STDOUT: {node_index: 4, kind: 'FunctionDeclaration', text: 'fn', subtree_size: 5, children: [
+// CHECK:STDOUT:   {node_index: 0, kind: 'DeclaredName', text: 'F'},
+// CHECK:STDOUT:   {node_index: 2, kind: 'ParameterList', text: '(', subtree_size: 2, children: [
+// CHECK:STDOUT:     {node_index: 1, kind: 'ParameterListEnd', text: ')'}]},
+// CHECK:STDOUT:   {node_index: 3, kind: 'DeclarationEnd', text: ';'}]},
+// CHECK:STDOUT: {node_index: 5, kind: 'FileEnd', text: ''},
+// CHECK:STDOUT: ]
+
+fn F();