Add Dump functions to Check, Parse, and Lex (#4669)

- Provide `Check::Dump(context, arg)` and similar.
- gdb and lldb should do contextual lookup, and `call Dump(*this,
Lex::TokenIndex::Invalid)` has been tested with gdb.
- Since this is only for debug, keeps the functions fully separated from
code.
- Uses alwayslink to ensure objects are correctly linked, even though
there are no calls.
- `-Wno-missing-prototypes` is needed when we don't have forward
declarations.
- Code is not linked in opt builds, using `#ifndef NDEBUG`.
- This probably could be doing something in BUILD files with a
`select()`, but the `#ifndef` seemed easier.

This is based on #4620, but uses free functions instead of member
functions.

Co-authored-by: Dana Jansens <danakj@orodu.net>

---------

Co-authored-by: danakj <danakj@orodu.net>

toolchain/parse/dump.cpp

@@ -0,0 +1,39 @@
+// 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
+
+#ifndef NDEBUG
+
+#include "toolchain/parse/dump.h"
+
+#include "common/ostream.h"
+#include "toolchain/lex/dump.h"
+
+namespace Carbon::Parse {
+
+auto DumpNoNewline(const Tree& tree, NodeId node_id) -> void {
+  if (!node_id.is_valid()) {
+    llvm::errs() << "NodeId(invalid)";
+    return;
+  }
+
+  auto kind = tree.node_kind(node_id);
+  auto token = tree.node_token(node_id);
+
+  llvm::errs() << "NodeId(kind: " << kind << ", token: ";
+  Lex::DumpNoNewline(tree.tokens(), token);
+  llvm::errs() << ")";
+}
+
+LLVM_DUMP_METHOD auto Dump(const Tree& tree, Lex::TokenIndex token) -> void {
+  Lex::Dump(tree.tokens(), token);
+}
+
+LLVM_DUMP_METHOD auto Dump(const Tree& tree, NodeId node_id) -> void {
+  DumpNoNewline(tree, node_id);
+  llvm::errs() << '\n';
+}
+
+}  // namespace Carbon::Parse
+
+#endif  // NDEBUG