Support for keyboard navigation of Autocomplete options.

Fixes the dartpad examples on the docs site.

Update samples to use repo analysis options, Fix sample templates and a ton of analyzer issues (#77868)

* Material Autocomplete widget

Allows passing in a TextEditingController and FocusNode to RawAutocomplete, which enables split UIs where the TextField is in another part of the tree from the results.

We are standardizing around the term Raw for lower level widgets.

A new widget that chooses an item from a list based on text input. Just the core widget, with Material and Cupertino versions to come.