Disable new SWIG string helper functions (#1145)

Author: a-maurice

cmake/firebase_swig.cmake

@@ -154,6 +154,10 @@ macro(firebase_swig_add_library name)
     # https://github.com/swig/swig/issues/672#issuecomment-400577864
     final=
     USE_EXPORT_FIX
+    # SWIG 4.3 added a C# class, SWIGStringWithLengthHelper, but is missing
+    # the corresponding C++ symbols, which can cause issues. We don't
+    # rely on this class anyway, so just disable it.
+    SWIG_CSHARP_NO_STRING_WITH_LENGTH_HELPER
   )
 
   set_property(TARGET ${name} PROPERTY SWIG_GENERATED_COMPILE_DEFINITIONS

docs/readme.md

@@ -71,6 +71,11 @@ Support
 
 Release Notes
 -------------
+### Upcoming
+- Changes
+    - General: Remove unresolved SWIG string symbols.
+      ([#1139](https://github.com/firebase/firebase-unity-sdk/issues/1139)).
+
 ### 12.4.0
 - Changes
     - General: Update to Firebase C++ SDK version 12.4.0.