Add wp-block-paragraph class to core/paragraph block

[hbhalodia]

What?

Issue - #46863

Why?

• By this PR, we are adding the common class name to the core/paragraph block, so that global styles that change for core/paragraph block applies only for that particular block and not to any other core/block.

How?

• This PR adds the new class wp-block-paragraph to all core/paragraph block. Validation error is being handled by adding this class using render_callback same as for heading block.

Testing Instructions

1. Open the site editor.
2. Go to any template or parts.
3. Go to styles section and change the global style for the core/paragraph block.
4. You can see that it only affects the core/paragraph block, earlier it was not the case.
5. Refer to the recording for before and after change.

Testing Instructions for Keyboard

• None.

Screenshots or screencast

Before

Before.Fix.-.core_paragraph.webm

After

After.Fix.-.Core_Paragraph.webm

[github-actions]

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• Type-related labels to choose from: [Type] Automated Testing, [Type] Breaking Change, [Type] Bug, [Type] Build Tooling, [Type] Code Quality, [Type] Copy, [Type] Developer Documentation, [Type] Enhancement, [Type] Experimental, [Type] Feature, [Type] New API, [Type] Task, [Type] Performance, [Type] Project Management, [Type] Regression, [Type] Security, [Type] WP Core Ticket, Backport from WordPress Core.
• Labels found: [Block] Paragraph.

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