Move bold/italic parser tests from Parsoid's whitelist into upstream.

Move bold/italic parser tests from Parsoid's whitelist into upstream.

Parsoid has been maintaining a whitelist for tests where its output
diverges from the PHP parser.  This patch upstreams part of that whitelist,
creating separate PHP and Parsoid test cases to document in one place
where the parsed output diverges and why.  (Uses the recently-added
'php' and 'parsoid' options in parserTests.)

Change-Id: I07ca6ec1e039a2842c641fe543b2d92eb964d932