MatAutoComplete is not allowed to be attached to the form

[jimmyzzxhlh]

Bug, feature request, or proposal:

Feature request

What is the current behavior?

Currently the MatAutoComplete component is attached to the input box, not the form. If the form contains other visible elements (e.g. in a search box there might be a search button as well as an X button for clearing the input text), then the auto-completed box is not going to be aligned with the input box.

What is the expected behavior?

Allow the input box to be resized with the form.

What are the steps to reproduce?

https://stackblitz.com/edit/angular-material2-issue-thhpo5

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