forminput: Enable Comma Seperated List in #forminput parser function
Enabled #forminput to take a comma seperated list of forms as value
for "form=" parameter. The dropdown menu now shows only forms from
the list. Also added support for form names that contain a comma.
Bug: T187110
Change-Id: I615bdf1da6b01ff3587f43f4282422fa71c3abaa