Accessibility: Adding pass-through for accessibility props.

[meatnordrink]

Swiping presents accessibility challenges. One of these challenges is that screen reader users may not be aware that content is swipeable, as the visual indication (Dots, in this case), is invisible to them.

This PR adds the React Nativeaccessible and accessibilityLabel props for pass-through to the <View> container within the <Dots> element. This allows devs to make the dots accessible by screen reader, and to add an accessible label indicating that there is swipeable content on the page.

Note that putting these properites on the pager view itself generally doesn't work, for the following reasons:

1. It's semantically incorrect. Pager views don't, by themselves, tell sighted users that there is swipeable content. Generally there are other visual indicators (arrow buttons or dots). To maintain parity between the sighted and assistive experience, visual indicators for sighted users should also be what communicates to users of assistive technology that there is swipeable content.
2. VoiceOver, on iOS, will treat any element that has accessible={true} as a single element, and not read or allow a screen reader to access any content inside. So placing an accessible prop and accessibilityLabel on the pager view itself results in loss of access to the content within the pager for users of assistive technology.

Adding an accessible label to the <Dots> element is a superior solution. And while it can already be done by adding a wrapper <View> around the <Dots> package, that results in an unnecessary <View> in the page hierarchy. This PR allows adding accessibility props without adding an additional <View>.

[yasaricli]

Thanks @meatnordrink, I will check it out and get back to you as soon as possible.