Document event inheritance

[rigor789]

Opening due to https://github.com/nativescript-vue/nativescript-vue.org/pull/213

We don't currently mention how events are inherited from base classes in NativeScript, which leads to confusion around available events for elements.

On individual element docs, we are only listing the events specific to an element (not inherited events), as otherwise the list would be too large and duplicated across a lot of different pages.