Rename parser dir to parse (#3178)

Continuing with #3070. Just a dir and file rename (mostly removing
prefixes, although for parse_tree_fuzzer and parse_tree_file_test I'm
dropping "tree" instead of "parse"). Everything in the parse dir should
be marked as a move.

toolchain/parse/handle_code_block.cpp

@@ -0,0 +1,41 @@
+// 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/parse/context.h"
+
+namespace Carbon::Parse {
+
+auto HandleCodeBlock(Context& context) -> void {
+  context.PopAndDiscardState();
+
+  context.PushState(State::CodeBlockFinish);
+  if (context.ConsumeAndAddLeafNodeIf(Lex::TokenKind::OpenCurlyBrace,
+                                      NodeKind::CodeBlockStart)) {
+    context.PushState(State::StatementScopeLoop);
+  } else {
+    context.AddLeafNode(NodeKind::CodeBlockStart, *context.position(),
+                        /*has_error=*/true);
+
+    // Recover by parsing a single statement.
+    CARBON_DIAGNOSTIC(ExpectedCodeBlock, Error, "Expected braced code block.");
+    context.emitter().Emit(*context.position(), ExpectedCodeBlock);
+
+    context.PushState(State::Statement);
+  }
+}
+
+auto HandleCodeBlockFinish(Context& context) -> void {
+  auto state = context.PopState();
+
+  // If the block started with an open curly, this is a close curly.
+  if (context.tokens().GetKind(state.token) == Lex::TokenKind::OpenCurlyBrace) {
+    context.AddNode(NodeKind::CodeBlock, context.Consume(), state.subtree_start,
+                    state.has_error);
+  } else {
+    context.AddNode(NodeKind::CodeBlock, state.token, state.subtree_start,
+                    /*has_error=*/true);
+  }
+}
+
+}  // namespace Carbon::Parse