docs-bug(INPUT): matNativeControl vs matInput input disambiguation

### Documentation Feedback

It's not apparent what a matNativeControl is, what the differences to matInput are, or what problem it solves.
The documentation for with matNativeControl is thrown in with matInput on one page without ever mentioning why to use one over the other.
It comes out of nowhere after showing a matInput in your example, first thing on the page.
Please amend the Input/FormField pages to clarify this selector.

### Affected documentation page

https://material.angular.io/components/input/overview

Read the Input overview documentation at material.angular.io/components/input/overview, including the Input and FormField pages and the existing matNativeControl and matInput examples. Clarify what matNativeControl is, how it differs from matInput, and when to use it; done means the selector's purpose and choice are apparent before the example appears.

Written by the indexing model from the issue text.