Fix possible recursive embeds in Dashboard text panels

Summary:
We currently detect tab panels embedding themselves, but do not detect text panels embedding themselves with {Wxx}.

Detect these self-embedding panels.

I had to add a bit of a hack to pass the parent panel PHIDs to the rule. Generally, I got the Markup API kind of wrong and want to update it, I'll file a followup with details about how I'd like to move forward.

Test Plan:
Created a text panel embedding itself, a tab panel embedding a text panel embedding itself, a tab panel embedding a text panel embedding the tab panel, etc.

Rendered all panels standalone and as {Wxx} from a different context.

Reviewers: chad, jbeta

Reviewed By: chad, jbeta

Differential Revision: https://secure.phabricator.com/D13999