Block Support: Change block visibility support key

[t-hamano]

Trac ticket: https://core.trac.wordpress.org/ticket/64272

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[github-actions]

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Props wildworks, andrewserong.

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[github-actions]

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[andrewserong]

LGTM, I like this approach of changing the name of the block support but keeping the block attribute the same. Ttested as part of reviewing the fix in WordPress/gutenberg#73432.

[github-actions]

A commit was made that fixes the Trac ticket referenced in the description of this pull request.

SVN changeset: 61285
GitHub commit: cd301d0

This PR will be closed, but please confirm the accuracy of this and reopen if there is more work to be done.