include the otel header-only part directly for ease of use

ext/opentelemetry-cpp-api-only/include/opentelemetry/common/string_util.h

@@ -0,0 +1,42 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+#pragma once
+
+#include "opentelemetry/nostd/string_view.h"
+#include "opentelemetry/version.h"
+
+OPENTELEMETRY_BEGIN_NAMESPACE
+namespace common
+{
+
+class StringUtil
+{
+public:
+  static nostd::string_view Trim(nostd::string_view str, size_t left, size_t right) noexcept
+  {
+    while (left <= right && isspace(str[left]))
+    {
+      left++;
+    }
+    while (left <= right && isspace(str[right]))
+    {
+      right--;
+    }
+    return str.substr(left, 1 + right - left);
+  }
+
+  static nostd::string_view Trim(nostd::string_view str) noexcept
+  {
+    if (str.empty())
+    {
+      return str;
+    }
+
+    return Trim(str, 0, str.size() - 1);
+  }
+};
+
+}  // namespace common
+
+OPENTELEMETRY_END_NAMESPACE