Send props to Dashicon.

[etoledom]

This PR is a continuation of #13977, and was simplified thanks to this suggestion: #13977 (comment) from @aduth .

gutenberg-mobile side PR: wordpress-mobile/gutenberg-mobile#628

Dashicon was modified to allow set colors and style on Mobile.
With these modifications, we can now do this:

<ToolbarButton
	label={ __( 'Add block' ) }
	icon={ ( <Dashicon icon="plus-alt" style={ styles.addBlockButton } color={ styles.addBlockButton.color } /> ) }
	onClick={ onInsertClick }
	iconProps={ { style: styles.addBlockButton, color: styles.addBlockButton.color } }
/>

And let ToolbarButton (or IconButton) use a Dashicon component setup on any way we need it to.

I will modify https://github.com/WordPress/dashicons/tree/master/sources/react after this PR gets merged.

[Tug]

I feel we've came back to the original logic now, I don't feel the proposed changes either improve or decrease the quality or logic of the code. Am I missing something?

[Tug]

Ok those were changes suggested in #13977

LGTM 🚢

[gziolo]

This is what we discussed in #13977. Let's 🚢 Thanks for wrangling it 🙇

[aduth]

It's not clear to me from the follow-up work whether it's still intended to remove ariaPressed as a prop of Dashicon.