Preserve original data inside parameter objects too

Parsoid has added a "key" property to parameter objects,
so now we have to preserve that rather than regenerating
all parameter objects.

Do this by changing the existing use of this.originalData
to a deep extend.

Change-Id: Ib4d31c2e0f7b567da1a148b51c42e688a2590b8e
Bonus: avoid modifying this.originalData
(cherry picked from commit a054a753bedc464e78fc32fc2533858b751c87c4)
Merge "Preserve original data inside parameter objects too" into wmf/1.25wmf6