feat: implementation of gsl::dyn_array (#1228)

* feat: implementation of gsl::dyn_array

Implement gsl::dyn_array<T, Allocator> as specified by the
CppCoreGuidlines here:
https://github.com/isocpp/CppCoreGuidelines/blob/master/docs/dyn_array.md

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

include/gsl/pointers

@@ -1,3 +1,4 @@
+// -*- C++ -*-
 ///////////////////////////////////////////////////////////////////////////////
 //
 // Copyright (c) 2015 Microsoft Corporation. All rights reserved.
@@ -357,7 +358,7 @@ auto make_strict_not_null(T&& t) noexcept
     return strict_not_null<std::remove_cv_t<std::remove_reference_t<T>>>{std::forward<T>(t)};
 }
 
-#if (defined(__cpp_deduction_guides) && (__cpp_deduction_guides >= 201611L))
+#if defined(__cpp_deduction_guides) && (__cpp_deduction_guides >= 201703L)
 
 // deduction guides to prevent the ctad-maybe-unsupported warning
 template <class T>
@@ -365,7 +366,7 @@ not_null(T) -> not_null<T>;
 template <class T>
 strict_not_null(T) -> strict_not_null<T>;
 
-#endif // ( defined(__cpp_deduction_guides) && (__cpp_deduction_guides >= 201611L) )
+#endif // defined(__cpp_deduction_guides) && (__cpp_deduction_guides >= 201703L)
 
 } // namespace gsl