docs: Javadoc fixes

A summary line failed to end with a period, with catastrophic
results--a table got pulled into the Javadoc summary table, which
broke the whole page's formatting. Putting a period at the end of
the summary line fixed everything.

Also made some other Javadoc fixes while I was in there--some
angle brackets needed to be escaped to display properly.

Doc is staged to:

http://go/dac-stage/reference/android/R.styleable

Bug: 119539013
Test: make ds-docs
Change-Id: If44050d8b03e70e619f0a2588ebc3ab07db7c4f2
Exempt-From-Owner-Approval: Doc-only change