[webview] rename unresponsive renderer APIs

Followup from API council review:

* Rename Renderer to RenderProcess for consistency with existing APIs.
* Make WebViewRenderProcess constructor public.
* Document 5 second minimum interval between successive callbacks.

Bug: 124767616
Bug: 123629980
Test: atest 'CtsWebkitTestCases'
Change-Id: I4416a97e8bb449c4a14a3617ef72a49c92aa3a83
6 files changed