bug(input): only apply MatInput styles when inside of a form-field

[jelbourn]

MatFormFieldincludes styles that affect theMatInputelement inside. However, some people useMatInput(such as withMatChipInput) without MatFormField, meaning that the styles only apply when some other MatFormField` appears on the page.

We should conditionally apply the MatInput CSS class used for styling based on whether it actually appears inside of a MatFormField. We probably want to leave the existing class as-is and move the styles to a new conditional class, since that will be the least breaking. This is still a potentially breaking change, though, so we'll have to see how severely this breaks apps inside of Google.