tl_expected: Add error_or functions

These are in C++23's std::expected, but were missing in our C++20
-capable copy.

Change-Id: I6a9bf0f62f7571bbb376361134757ea36c9e49f3
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>

src/libs/3rdparty/tl_expected/include/tl/expected.hpp

@@ -2039,6 +2039,19 @@ public:
                   "T must be move-constructible and convertible to from U&&");
     return bool(*this) ? std::move(**this) : static_cast<T>(std::forward<U>(v));
   }
+
+  template <class U> constexpr T error_or(U &&v) const & {
+    static_assert(std::is_copy_constructible<E>::value &&
+                      std::is_convertible<U &&, E>::value,
+                  "E must be copy-constructible and convertible to from U&&");
+    return !has_value() ? err().value() : static_cast<T>(std::forward<U>(v));
+  }
+  template <class U> TL_EXPECTED_11_CONSTEXPR T error_or(U &&v) && {
+    static_assert(std::is_move_constructible<T>::value &&
+                      std::is_convertible<U &&, T>::value,
+                  "E must be move-constructible and convertible to from U&&");
+    return !has_value() ? std::move(err().value()) : static_cast<E>(std::forward<U>(v));
+  }
 };
 
 namespace detail {