Block Settings Menu: Don't render 'Move to' if there is only one block.

[getsource]

Description

In the Block Settings Menu, instead of disabling, don't render "Move to" when there is only one block.

This is a follow-up for consideration from #33135 and this comment from @mtias.

Other items in the Block Settings Dropdown aren't displayed when they aren't actionable.

Assuming there are no a11y concerns, I like the idea of further reducing noise and interface elements when possible.

See: #33029, #33135

How has this been tested?

Using wp-env:

• Check to confirm "Move to" is disabled with one block
• Add another block
• Check to confirm "Move to" is enabled and functions
• Remove one block
• Check to confirm "Move to" is disabled again.

Also tested with npm run test.

Screenshots

The current/before behavior can be seen in the video at the top of #33135.

Proposed Change:

Screen.Recording.2021-07-02.at.16.22.16.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!

[mtias]

Other items in the Block Settings Dropdown aren't displayed when they aren't actionable.

Also the movers and drag handle themselves are not shown when a single block is in place, so this is consistent.