Split executable semantics fuzzer into cc_binary and cc_test

This is a workaround for #1208, allowing to remove manual tag to allow building and testing fuzzer code during precommits and in bazel test ...

Tested:
bazel test -k ...
bazel build -c opt executable_semantics/fuzzing:executable_semantics_fuzzer
bazel-bin/executable_semantics/fuzzing/executable_semantics_fuzzer

executable_semantics/fuzzing/fuzzer_util_test.cpp

@@ -0,0 +1,47 @@
+// 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 "executable_semantics/fuzzing/fuzzer_util.h"
+
+#include <gmock/gmock.h>
+#include <google/protobuf/text_format.h>
+#include <gtest/gtest.h>
+
+#include <fstream>
+
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/raw_ostream.h"
+
+namespace Carbon::Testing {
+namespace {
+
+static std::vector<llvm::StringRef>* carbon_files = nullptr;
+
+// A workaround for https://github.com/carbon-language/carbon-lang/issues/1208.
+TEST(FuzzerUtilTest, RunFuzzerOnCorpus) {
+  int file_count = 0;
+  for (const llvm::StringRef f : *carbon_files) {
+    llvm::outs() << "Processing " << f << "\n";
+    std::ifstream file(f.str(), std::ios::in);
+    ASSERT_TRUE(file.is_open());
+    std::stringstream contents;
+    contents << file.rdbuf();
+    Fuzzing::Carbon carbon_proto;
+    ASSERT_TRUE(google::protobuf::TextFormat::ParseFromString(contents.str(),
+                                                              &carbon_proto));
+    ParseAndExecute(carbon_proto.compilation_unit());
+    ++file_count;
+  }
+  EXPECT_GT(file_count, 0);
+}
+
+}  // namespace
+}  // namespace Carbon::Testing
+
+auto main(int argc, char** argv) -> int {
+  ::testing::InitGoogleTest(&argc, argv);
+  Carbon::Testing::carbon_files =
+      new std::vector<llvm::StringRef>(&argv[1], &argv[argc]);
+  return RUN_ALL_TESTS();
+}