Toolbars: Fix title behavior in UI

[shilman]

Closes N/A

Reported here https://discord.com/channels/486522875931656193/1105749672489918506

What I did

There's a bug in Storybook 7 where the toolbar button automatically shows a text label even if no title is specified in the toolbar configuration. It also makes a deprecation warning in the console. This PR fixes that. Now if the user doesn't specify a title attribute for the toolbar, no label is shown, and no deprecation warning is shown.

It also fixes a few other minor bugs in the same code:

• If no title or icon is specified, it will warn in the browser console
• If the user uses a reset toolbar item
  • it won't show the reset label when dynamicTitles is set
  • it won't show a react duplicate key warning in the browser console

Self-merging @valentinpalkovic

How to test

Run a sandbox and check out the toolbar. In the current code both Theme and Locale will show up as labels. With this PR, the Locale label goes away since it's not configured in the project.

[gilbarbara]

Yes! Thank you!