Compile folly's SanitizeLeak.cpp in Fantom's tester

## Summary:

Fantom's tester doesn't link when it's built with AddressSanitizer. Under `-fsanitize=address`, folly headers like `small_vector.h` and `Singleton.h` call `folly::detail::annotate_object_leaked_impl` and `annotate_object_collected_impl`, and only `folly/memory/SanitizeLeak.cpp` defines them. Fantom's folly build compiles `SanitizeAddress.cpp` and `SanitizeThread.cpp` but not that file, so the link fails on both symbols.

This adds `folly/memory/SanitizeLeak.cpp` to `folly_runtime_SRC`, which the `RCT-Folly` podspec already compiles. Without ASan the file only defines those functions, nothing calls them.

Fixes #59668

## Changelog:

[INTERNAL] [FIXED] - Fix Fantom tester link under AddressSanitizer by compiling folly's SanitizeLeak.cpp

## Test Plan:

I couldn't run the full Fantom build here, so I checked the link against folly v2024.11.18.00 (the version Fantom pins) with clang and `-fsanitize=address`. A small program using `folly::small_vector`, linked with the `folly_runtime` sources it needs, fails with undefined `annotate_object_leaked_impl` / `annotate_object_collected_impl`. Adding `SanitizeLeak.cpp` makes it link and run.

Differential Revision: D128600166

Pull Request resolved: #59674

Author: lazerg

private/react-native-fantom/tester/third-party/folly/CMakeLists.txt

@@ -48,6 +48,7 @@ SET(folly_runtime_SRC
         folly/lang/SafeAssert.cpp
         folly/lang/ToAscii.cpp
         folly/memory/SanitizeAddress.cpp
+        folly/memory/SanitizeLeak.cpp
         folly/memory/detail/MallocImpl.cpp
         folly/net/NetOps.cpp
         folly/portability/SysUio.cpp