Inserter: In text label mode, use "Close" label when inserter is open.

[getsource]

Description

In text label mode, changes inserter label from "Add" to "Close" when the inserter is opened.

Initial review props @Mamaduka.
Fixes: #33397

How has this been tested?

Using wp-env:

• In Options -> Preferences -> Appearance, enable "Display Button Labels"
• Click "Add" to open Inserter
• Notice that "Add" changes to "Close"
• Click "Close" to close Inserter
• Notice that "Close" changes back to "Add"

Also, ran npm run test locally.

Screenshots

Before is visible in #33397

After (Narrow Viewport, like I assume was the case in the original issue -- only shows Add):

Screen.Recording.2021-07-19.at.16.19.46.mov

After (Wide Viewport -- shows all buttons):

Screen.Recording.2021-07-19.at.16.23.10.mov

Types of changes

Enhancement

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).

[ntsekouras]

Looks good! Thanks!

[ntsekouras]

Actually I'm seeing this:

Let's check this a bit better before landing