Split semantics into check and sem_ir directories (#3176)

Continuing along with #3070. Note this is just a file rename, with BUILD
edits; every file previously in semantics/ should show as moved (except
maybe BUILDs, which split).

toolchain/check/node_stack.cpp

@@ -0,0 +1,28 @@
+// 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
+
+#include "toolchain/check/node_stack.h"
+
+#include "llvm/ADT/STLExtras.h"
+#include "toolchain/sem_ir/node.h"
+
+namespace Carbon::Check {
+
+auto NodeStack::PrintForStackDump(llvm::raw_ostream& output) const -> void {
+  output << "NodeStack:\n";
+  for (auto [i, entry] : llvm::enumerate(stack_)) {
+    auto parse_node_kind = parse_tree_->node_kind(entry.parse_node);
+    output << "\t" << i << ".\t" << parse_node_kind;
+    if (parse_node_kind == Parse::NodeKind::PatternBinding) {
+      output << " -> " << entry.name_id;
+    } else {
+      if (entry.node_id.is_valid()) {
+        output << " -> " << entry.node_id;
+      }
+    }
+    output << "\n";
+  }
+}
+
+}  // namespace Carbon::Check