[web] Save the autofill information (flutter#20256)

* changes for autofill. Commit save=false works. added submit button. set form actions

* save the forms on the dom

* fix tests. fix input element location. fix single element forms

* fix failing ios test. add more unit test methods for submitting the form

* address reviewer comments

* remove only the forms from the map

* remove debug line

* fix issues with login info saving. format file

* fix textarea id. fix unit tests methods

* remove debug line

* fixes flickering in safari. remove an unnecessary secind append in firefox

* address reviewer comments

* address reviewer comments