Fix: custom block view rendering freezes the Backoffice

[andrejd22]

Prerequisites

• I have added steps to test this contribution in the description below

If there's an existing issue for this PR then this fixes

Description

Fixes #19297
Fixes #16994

[github-actions]

Hi there @andrejd22, thank you for this contribution! 👍

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[Copilot]

Pull Request Overview

This PR fixes an issue with custom block view rendering in the Umbraco CMS frontend. The changes ensure that custom block views are properly rendered when no extensions are found, while maintaining fallback to built-in block views.

Key Changes:

• Added a defaultRenderMethod property to extension slots for fallback rendering
• Modified block grid entry to use the new default render method instead of slot content
• Ensured proper rendering flow when custom block views are not available

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
extension-slot.element.ts	Added defaultRenderMethod property and logic to use it as fallback when no permitted extensions exist
block-grid-entry.element.ts	Updated to use the new default render method approach instead of slot content for built-in block view rendering

[iOvergaard]

• Ran the formatter to ensure the code is in line with the formatting rules.
• Changed the new render method to be a class property instead (#method = () => {}) so it works with private properties (caught in production mode by the e2e tests)

LGTM

[nielslyngsoe]

Hi @andrejd22

I just wanted to say thanks for the contribution, and mention that the implementation was well done. 👏

Thanks!

[nielslyngsoe]

I took the freedom to rename the method and extend the work to the other Block Editors, you can see more on this PR: #20005