Moar Autofill Framework javadoc improvements:

- Fixed WebView < > and API calls.
- Improved description of virtual views.
- Described how to set boundaries of virtual views.
- Improved AUTOFILL_FLAG_INCLUDE_NOT_IMPORTANT_VIEWS doc.

Bug: 37567048
Test: ran 'm -j doc-comment-check-docs' and checked resulting HTML

Change-Id: Ic0d1e9ff2703c87d4007f0092a2f8dfe0efca6db