Widget inserter: Clarify that the button toggles the inserter

[walbo]

Description

Follow-up on #29759
Add the same functionality to the inserter button on the widget screen and rename the label.

How has this been tested?

Locally by toggling the inserter sidebar.

Screenshots

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).

[Mamaduka]

This looks good. Thanks, @walbo!

[draganescu]

👋🏻 how come we need to implement this in this specific editor? Isn't that application header common accross all editors?

[walbo]

👋🏻 how come we need to implement this in this specific editor? Isn't that application header common accross all editors?

Seems like the same functionality is implementet both in edit-post and edit-site package. As you say these should probably be aligned in a common component.

I can create a alternative PR later today that explores shared code.

[Mamaduka]

I had a similar question about the different component a few months ago - #31597 (comment).

TL;DR - Sometimes duplication is better than bad early abstraction.