Editor: Correctly mark ToolsMoreMenuGroup as a private SlotFill

[Mamaduka]

What?

PR updates ToolsMoreMenuGroup slot-fill and correctly mark them as private, preventing them from leaking to consumers using string names. This matches ViewMoreMenuGroup.

Testing Instructions

None. There are no behavioral changes to consumers

[github-actions]

Size Change: +1 B (0%)

Total Size: 7.71 MB

📦 View Changed

Filename	Size	Change
build/scripts/editor/index.min.js	530 kB	+1 B (0%)

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[youknowriad]

Do we know if there are actual users of this in the wild?

[github-actions]

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Co-authored-by: Mamaduka <mamaduka@git.wordpress.org>
Co-authored-by: youknowriad <youknowriad@git.wordpress.org>

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[Mamaduka]

Do we know if there are actual users of this in the wild?

Hard to say, directory search returns nothing.

I fixed a similar leak two years ago, and no reports for it - #67271.

[youknowriad]

Directory not returning anything is a good sign.