Rename semantic to sem

* Rename namespace semantic to sem
* Rename directory src/semantic/ to src/sem/

Bug: tint:724
Change-Id: I76383b821fbca7f1037a803c497b595a706dcb06
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/48120
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>

src/sem/sem_statement.cc

@@ -0,0 +1,39 @@
+// Copyright 2021 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <algorithm>
+
+#include "src/ast/block_statement.h"
+#include "src/debug.h"
+#include "src/sem/statement.h"
+
+TINT_INSTANTIATE_TYPEINFO(tint::sem::Statement);
+
+namespace tint {
+namespace sem {
+
+Statement::Statement(const ast::Statement* declaration,
+                     const ast::BlockStatement* block)
+    : declaration_(declaration), block_(block) {
+#ifndef NDEBUG
+  if (block) {
+    auto& stmts = block->statements();
+    TINT_ASSERT(std::find(stmts.begin(), stmts.end(), declaration) !=
+                stmts.end());
+  }
+#endif  //  NDEBUG
+}
+
+}  // namespace sem
+}  // namespace tint