Fix macOS/iOS build errors due to missing NS_SWIFT_SENDABLE macro definition

[tustanivsky]

During a recent attempt to publish the plugin package to the Unreal Engine Marketplace the following errors occurred:

Users/build/Build/U5M-Marketplace-Mac/Sync/LocalBuilds/PluginTemp/HostProject/Plugins/Sentry/Source/ThirdParty/Mac/include/Sentry/SentryOptions.h:145:79: error: expected ';' at end of declaration list
@property (nullable, nonatomic, copy) SentryBeforeSendEventCallback beforeSend NS_SWIFT_SENDABLE;

/Users/build/Build/U5M-Marketplace-Mac/Sync/LocalBuilds/PluginTemp/HostProject/Plugins/Sentry/Source/ThirdParty/Mac/include/Sentry/SentryOptions.h:145:80: error: C++ requires a type specifier for all declarations
@property (nullable, nonatomic, copy) SentryBeforeSendEventCallback beforeSend NS_SWIFT_SENDABLE;

/Users/build/Build/U5M-Marketplace-Mac/Sync/LocalBuilds/PluginTemp/HostProject/Plugins/Sentry/Source/ThirdParty/Mac/include/Sentry/SentryOptions.h:145:80: error: cannot declare variable inside @interface or @protocol
@property (nullable, nonatomic, copy) SentryBeforeSendEventCallback beforeSend NS_SWIFT_SENDABLE;

...

fatal error: too many errors emitted, stopping now [-ferror-limit=]
20 errors generated.
[3/9] Compile Module.Sentry.1_of_3.cpp
[4/9] Compile Module.SentryEditor.cpp
[5/9] Compile Module.Sentry.3_of_3.cpp
[6/9] Link UnrealEditor-Sentry.dylib cancelled
[7/9] Link UnrealEditor-SentryEditor.dylib cancelled
[8/9] WriteMetadata UnrealEditor.target cancelled
[9/9] sh Executing post build script (PostBuild-1.sh)
Sentry: Symbol upload script is missing. Skipping post build step.
Took 33.12142s to run dotnet, ExitCode=6
UnrealBuildTool failed. See log for more details. (/Users/build/Build/U5M-Marketplace-Mac/Sync/Engine/Programs/AutomationTool/Saved/Logs/BuildMarketPlaceItems/UBT-UnrealEditor-Mac-Development.txt)
AutomationTool executed for 0h 0m 33s
AutomationTool exiting with ExitCode=6 (6)
RunUAT ERROR: AutomationTool was unable to run successfully. Exited with code: 6
Took 34.26s to run RunUAT.sh, ExitCode=6
Build failed for plugin Sentry_5.1

The build farms where plugin pre-compilation for UE 5.1 occurs might be using an older version of Xcode (pre-13) or targeting an older macOS version (pre-12) where the NS_SWIFT_SENDABLE macro is unavailable. Adding a check to verify if the macro is defined should help address these issues.