Replace std::is_trivially_assignable with `std::is_trivially_copy_a…

…ssignable`

pxr/base/vt/traits.h

@@ -44,10 +44,8 @@ struct VtIsArray : public std::false_type {};
 // space but do not have a trivial assignment are not cheap to copy.  E.g. std::
 // containers.  Clients can specialize this template for their own types that
 // aren't trivially assignable but are cheap to copy to enable local storage.
-// In C++17, std::is_trivially_copy_assignable<T> could be used in place of
-// std::is_trivially_assignable
 template <class T>
-struct VtValueTypeHasCheapCopy : std::is_trivially_assignable<T&, const T&> {};
+struct VtValueTypeHasCheapCopy : std::is_trivially_copy_assignable<T> {};
 
 #define VT_TYPE_IS_CHEAP_TO_COPY(T)                                            \
     template <> struct VtValueTypeHasCheapCopy<TF_PP_EAT_PARENS(T)>            \

pxr/base/vt/value.h

@@ -197,14 +197,12 @@ class VtValue
     typedef std::aligned_storage<
         /* size */_MaxLocalSize, /* alignment */_MaxLocalSize>::type _Storage;
 
-    // In C++17, std::is_trivially_copy_assignable<T> could be used in place of
-    // std::is_trivially_assignable
     template <class T>
     using _IsTriviallyCopyable = std::integral_constant<bool,
-        std::is_trivially_default_constructible<T>::value &&
-        std::is_trivially_copyable<T>::value &&
-        std::is_trivially_assignable<T&, const T&>::value &&
-        std::is_trivially_destructible<T>::value>;
+        std::is_trivially_default_constructible_v<T> &&
+        std::is_trivially_copyable_v<T> &&
+        std::is_trivially_copy_assignable_v<T> &&
+        std::is_trivially_destructible_v<T>>;
 
     // Metafunction that returns true if T should be stored locally, false if it
     // should be stored remotely.