fix: restore toolbar default items

[ndoschek]

What it does

• properly restore the toolbar items in the storage provider from the default factory and ensure to write to the config file
• ensure the defaults are restored on startup in case there is no config file yet
• in case the config file was corrupted, allow the user to restore the default toolbar items via an action in the error message popup
• chore: remove unused injections in ToolbarCommandContribution

Fixes #15231

How to test

• Use the "Restore Toolbar Defaults" command from the toolbar context menu and verify that:
  • The toolbar resets to the correct default items.
  • The toolbar.json config file reflects the default configuration (open via "Customize Toolbar (Open JSON)" command in the context menu
• Customize the toolbar by adding/removing items via the context menu and directly via the toolbar.json config file
• Save a corrupted toolbar config (like an empty file) and verify the correct error message is shown and allows to directly trigger the "Restore Toolbar Defaults" command
• Edit: If there is no or an empty config file on startup, the defaults should be restored automatically without the user error prompt

Follow-ups

x

Breaking changes

• This PR introduces breaking changes and requires careful review. If yes, the breaking changes section in the changelog has been updated.

Attribution

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[sgraband]

Thank you for this contribution! LGTM and works great! 👍

Especially nice that you now get notified, when the config does not work!