Template Part: Add layout support

[himanshupathak95]

What?

Part of: #43248

Add layout support to the Template Part block.

Why?

Currently, the Template Part block lacks layout controls.

How?

Added layout support by enabling it in the block's configuration ( block.json ). Since the Template Part block already uses useInnerBlocksProps, enabling the layout support property is sufficient to implement this feature.

"supports": {
    "layout": true
}

Testing Instructions

• Create or edit a template in the Site Editor
• Add a Template Part block
• Add blocks inside the Template Part (e.g., paragraphs, headings)
• Select the Template Part block
• Verify in the sidebar that:
  • Layout controls are now available
  • The justification is working as expected
  • The width modifications are working as expected

Screencast

Screen.Recording.2025-02-17.at.14.23.32.mov

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Co-authored-by: himanshupathak95 <[email protected]>
Co-authored-by: carolinan <[email protected]>

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[carolinan]

I don't think this change should be merged, because all options on this block has been omitted on purpose.
The intention is that the template part should remain a container block with all stying applied to the blocks that are inside it.

It is a long read, but here is one of the discussions that led to this decision: #30732
#30732 (comment)

There is also work on unifying the template part and patterns:
#57011