feat(runtime): add nullability annotations to NativeScript.h (#461)

* feat(runtime): add nullability annotations to NativeScript.h

Without them every pointer in the embedder API imports into Swift as
implicitly unwrapped, which hides the contract the implementation
already has: BaseDir, the script string and the Config argument are
required (their UTF8String feeds a std::string), while ApplicationPath,
MetadataPtr and Arguments are optional with defaults (BaseDir/app, the
__TNSMetadata section, no inspector arguments). initWithConfig: never
returns nil.

* fix(runtime): read no inspector flags from a nil Arguments array

Config.Arguments is optional, but ArgumentsCount was handed to the
inspector as is, so a nil array with a count above one made debug
startup index a null argv. Pass a count of 0 when the array is nil;
the argv loop keeps the C contract and trusts the count it is given.

Author: adrian-niculescu

NativeScript/NativeScript.h

@@ -1,14 +1,16 @@
 #import <Foundation/Foundation.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface Config : NSObject
 
 @property (nonatomic, retain) NSString* BaseDir;
-@property (nonatomic, retain) NSString* ApplicationPath;
-@property (nonatomic) void* MetadataPtr;
+@property (nonatomic, retain, nullable) NSString* ApplicationPath;
+@property (nonatomic, nullable) void* MetadataPtr;
 @property BOOL IsDebug;
 @property BOOL LogToSystemConsole;
 @property int ArgumentsCount;
-@property (nonatomic) char** Arguments;
+@property (nonatomic) char* _Nullable* _Nullable Arguments;
 
 @end
 
@@ -26,3 +28,5 @@
 - (bool)liveSync;
 
 @end
+
+NS_ASSUME_NONNULL_END

NativeScript/NativeScript.mm

@@ -193,7 +193,9 @@ - (instancetype)initializeWithConfig:(Config*)config {
           new v8_inspector::JsV8InspectorClient(runtime_);
       inspectorClient->init();
       inspectorClient->registerModules();
-      inspectorClient->connect([config ArgumentsCount], [config Arguments]);
+      // A nil Arguments array carries no inspector flags, whatever ArgumentsCount says.
+      inspectorClient->connect(config.Arguments != nullptr ? config.ArgumentsCount : 0,
+                               config.Arguments);
       Console::AttachInspectorClient(inspectorClient);
     }
   }