WebView: clean up onReceivedSslError docs

No change to logic, only docs.

This adds {@link}'s for references to SslErrorHandler methods, improving
readability. This also clarifies this API is only called for recoverable
errors.

Fixes: 123042566
Test: m offline-sdk-docs
Change-Id: I0e94c9903e638e2fce59f35ec76eb5566e7ad875