WebView: remove "</p>" tags from docs

Docs change only, no change to logic.

This removes closing "</p>" tags from WebView API docs, as per API
guidelines.

This also adds a trailing newline to a <pre> block for consistency.

Other than the modified <pre> block, this has no reader-visible change,
it merely complies with best practices from Android API guidelines.

Bug: 65381884
Test: make docs (and manually compare before/after for differences)
Change-Id: I2f911a43b88a8897d9d1b5c7945360580491883d