Update vibrator javadoc formatting.

After reviewing rendered docs, adding missing paragraph markers
and some small typos, as well as fixing code snippets to be inside a <pre> block. At the
moment, trailing newlines get picked up so it's also necessary to
terminate the code and pre blocks on the actual last line of code.

Test: built docs and manually reviewed site
Change-Id: I327b146eaae20fa3a2e8cf066e211e14cb165c51