Validate parse nodes correspond to expected tokens (#3295)

Can specify which tokens are allowed generally, and any additional
tokens that only occur when the parse node has an error.

---------

Co-authored-by: Richard Smith <richard@metafoo.co.uk>

toolchain/parse/node_kind.h

@@ -8,6 +8,7 @@
 #include <cstdint>
 
 #include "common/enum_base.h"
+#include "toolchain/lex/token_kind.h"
 
 namespace Carbon::Parse {
 
@@ -44,6 +45,11 @@ class NodeKind : public CARBON_ENUM_BASE(NodeKind) {
 // We expect the parse node kind to fit compactly into 8 bits.
 static_assert(sizeof(NodeKind) == 1, "Kind objects include padding!");
 
+// Validates that a `parse_node_kind` parser node can be generated for a
+// `lex_token_kind` lexer token.
+void CheckNodeMatchesLexerToken(NodeKind parse_node_kind,
+                                Lex::TokenKind lex_token_kind, bool has_error);
+
 }  // namespace Carbon::Parse
 
 #endif  // CARBON_TOOLCHAIN_PARSE_NODE_KIND_H_