Remove most of the metaprogramming in node.h in favor of listing all the members in the typed node structs. (#3310)

Split `node.h` into separate files for ID types (`id.h`) and for typed
nodes (`typed_nodes.h`). The per-node-kind data is now specified as part
of declaring the typed nodes, and is removed from the node kinds
x-macros, which now simply enumerate the node kinds.

toolchain/sem_ir/file.cpp

@@ -53,10 +53,10 @@ File::File(SharedValueStores& value_stores)
   // a normal type. Every other builtin is a type, including the
   // self-referential TypeType.
 #define CARBON_SEM_IR_BUILTIN_KIND(Name, ...)                      \
-  nodes_.push_back(Builtin(BuiltinKind::Name == BuiltinKind::Error \
+  nodes_.push_back(Builtin{BuiltinKind::Name == BuiltinKind::Error \
                                ? TypeId::Error                     \
                                : TypeId::TypeType,                 \
-                           BuiltinKind::Name));
+                           BuiltinKind::Name});
 #include "toolchain/sem_ir/builtin_kind.def"
 
   CARBON_CHECK(nodes_.size() == BuiltinKind::ValidCount)
@@ -82,7 +82,7 @@ File::File(SharedValueStores& value_stores, std::string filename,
   for (auto [i, node] : llvm::enumerate(builtins->nodes_)) {
     // We can reuse builtin type IDs because they're special-cased values.
     nodes_.push_back(
-        CrossReference(node.type_id(), BuiltinIR, SemIR::NodeId(i)));
+        CrossReference{node.type_id(), BuiltinIR, SemIR::NodeId(i)});
   }
 }
 
@@ -374,7 +374,8 @@ auto File::StringifyTypeExpression(NodeId outer_node_id,
       case StructTypeField::Kind: {
         auto field = node.As<StructTypeField>();
         out << "." << strings().Get(field.name_id) << ": ";
-        steps.push_back({.node_id = GetTypeAllowBuiltinTypes(field.type_id)});
+        steps.push_back(
+            {.node_id = GetTypeAllowBuiltinTypes(field.field_type_id)});
         break;
       }
       case TupleType::Kind: {