Combobox: Add component

[ItsJonQ]

We'll need a highly flexible Combobox component. Something as feature-rich (hopefully) as React Select.

Some of the features we'd need to support would include:

• Selecting multiple items (which render as deletable tags)
• Custom menu/item rendering
• Grouping
• Async loading/fetching support
• Portaling

We may be able to Downshift as the state management/interaction handler (the "brains" if you will) for this Combobox.

I know @diegohaz has been working on a Reakit Combobox as well <3.

[ItsJonQ]

An example of where a Combobox component is used within Gutenberg (adding tags).

[diegohaz]

By the way, the Reakit Combobox stories can be found here: https://next.reakit.io/storybook/?path=/story/examples--accessible-combobox

I'll create a tags example there. It's going to be fun! :D

[ItsJonQ]

I'll create a tags example there. It's going to be fun! :D

@diegohaz Can't wait!!!!

[diegohaz]

@ItsJonQ Built this: https://codesandbox.io/s/reakit-combobox-with-tags-smfgu

The code is a mess and it has probably a lot of bugs, but, yeah, it was fun! 😆

[ItsJonQ]

For integration with Gutenberg, we may need to replace the current FontSizePicker component from @wordpress/components (as it related to Typography Tools in Global Styles).

As such, we'll need some sort of Combobox component:

As such, we can probably role with the technologies/setup that the current CustomSelect from WP components has.

[ItsJonQ]

🤦 . I just realized that the current FontSizePicker doesn't use a ComboBox. But rather, a custom <Select /> component.

[ItsJonQ]

Creating a new issue for the custom select component:
#161