Add viewStyle property for block metadata

[gaambo]

Adds a viewStyle property for block metadata to allow registering stylesheets/handles, that will only be enqueued on the frontend if a block is rendered (not in the backend). Similar to viewScript.
See trac ticket for more information.

Trac ticket: 59673

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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.

[gziolo]

Let’s plan to include it in the upcoming WP 6.5.0 release. I need to take a closer look, but so far everything looks good.

[github-actions]

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[gziolo]

Committed with https://core.trac.wordpress.org/changeset/57493.