[cpp] move `ofInt64` `toInt64` from haxe.Int64 to cpp.Int64 to satisfy api generator

std/cpp/Int64.hx

@@ -22,4 +22,14 @@
 
 package cpp;
 
-@:coreType @:notNull @:runtimeValue abstract Int64 from Int to Int {}
+@:coreType @:notNull @:runtimeValue abstract Int64 from Int to Int {
+	@:to
+	#if !cppia inline #end function toInt64():haxe.Int64 {
+		return cast this;
+	}
+
+	@:from
+	static #if !cppia inline #end function ofInt64(x:haxe.Int64):Int64 {
+		return cast x;
+	}
+}

std/cpp/_std/haxe/Int64.hx

@@ -144,16 +144,6 @@ abstract Int64(__Int64) from __Int64 to __Int64 {
 		return __Int64.make(high, low);
 	}
 
-	@:to
-	#if !cppia inline #end function toInt64():cpp.Int64 {
-		return cast this;
-	}
-
-	@:from
-	static #if !cppia inline #end function ofInt64(x:cpp.Int64):Int64 {
-		return cast x;
-	}
-
 	@:from
 	public static #if !cppia inline #end function ofInt(x:Int):Int64 {
 		return __Int64.ofInt(x);