Enabled default block appender in gallery edit component

[dhruvikpatel18]

Followed PR of: #71204 (comment)

What?

This does seem like a good addition, similar to the Buttons block, and other design-related blocks such as Columns, Grid, and Group, which have an appender. The gallery block currently lacks one. so adding it would improve consistency.
If there’s enough consensus, should we raise a separate follow-up PR to address this?

By @im3dabasia

Screenshots or screencast

Before

After

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[Mamaduka]

Thanks for contributing, @dhruvikpatel18!

Can you include before/after screenshots for the PR.

[im3dabasia]

@dhruvikpatel18, when you have a moment, please rebase the PR with trunk so we can resolve the failing CI cases.

[Mamaduka]

@dhruvikpatel18, @im3dabasia, let's get more feedback before merging this. I checked some old issues, and it seems that having "Add new" in the toolbar was intentional. See: #21247 and #38036.

While consistency is the key, not all blocks are created equal, and we should also keep that in mind.

@glendaviesnz, I know it's been a while since the Gallery block refactoring, but do you have any additional details?