Add a test for avoiding a custom input accessory view

[KaneCheshire]

A custom input accessory view is a view (or view controller) that shows up above the keyboard, like the predictions bar. We should add a test to make sure our scrolling logic avoids that view too when keyboards are shown.

[KaneCheshire]

I've just had a look into this and there's two issues:

• First is that Apple don't add any identifier or type to an accessory view so there's no way for TTK to be able to check if one exists, unless we somehow provide a way for users to tell TTK the IDs they're using for their accessory views, or we require that accessory views have a specific ID set on them so that TTK can avoid them while scrolling
• Second is that when an accessory view is showing, for some reason our scroll view (MyScrollView) is being reported as existing but not hittable, so our scrolling logic completely fails since it's expecting it to be hittable. This doesn't happen when the keyboard is showing without an accessory view

[KaneCheshire]

I've pushed up a branch that adds the input accessory view so you can see: 491868c