Avoid use-after-return caused by double move

Summary:
Previously, `Result<T>`'s constructor used std::move(val) to initialize the
value. This resulted in an unnecessary extra move and destructor call on a
moved-from stack object, triggering an HWASAN stack tag mismatch when the
moved-from object was later destructed.

Replacing std::move(val) with just val avoids the extra move while preserving
correct semantics, since T is always a concrete type. This ensures only one
move occurs and avoids lifetime violations that can lead to tag mismatches
under HWASAN.

Differential Revision: D76271359

Author: Tamir Duberstein

runtime/core/result.h

@@ -70,8 +70,8 @@ class Result final {
   /// Value copy constructor.
   /* implicit */ Result(const T& val) : value_(val), hasValue_(true) {}
 
-  /// Value move constructor.
-  /* implicit */ Result(T&& val) : value_(std::move(val)), hasValue_(true) {}
+  /// Value rvalue reference constructor.
+  /* implicit */ Result(T&& val) : value_(val), hasValue_(true) {}
 
   /// Result move constructor.
   /* implicit */ Result(Result&& rhs) noexcept : hasValue_(rhs.hasValue_) {