#1863 [macOS] setCursor method in subclass of SCIContentView will not be called

[Tse Kit Yam]

I subclass SCIContentView in my app, and I found that the cursor style will not be chanegd according to the position. This is because Window only set cursor style to SCIContentView but not SCIContentView's subclasses. I think subclasses of SCIContentView have the right and need to get this style too.

In this patch I use -isKindOfClass instead of -isMemberOfClass to check the object type. If the object passed the tes, then the object should be able to cast to SCIContentView and the rest should be the same.

[Neil Hodgson]

Committed as [93a7d7].