refactor(engine-java): remove unused toJSNode/transformToJsNode methods

[GauBen]

Description

A leftover from the HBS era: we no longer need to manipulate plain JS objects in React, we can use Java objects

Checklist

Source code

• I've shared and documented any breaking change
• I've reviewed and updated the jahia-depends

Tests

• I've provided Unit and/or Integration Tests
• I've updated the parent issue with required manual validations

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[Copilot]

Pull request overview

This PR removes legacy code from the Handlebars (HBS) era that was used to convert JCR nodes into plain JavaScript objects. With the migration to React, the codebase now directly uses Java objects, making these transformation methods obsolete.

Changes:

• Removed three methods from JSNodeMapper that converted JCR nodes to JavaScript objects (toJSNode, toJSNodeProperties, toJSNodePropertyValue)
• Removed the transformToJsNode method from RenderHelper that wrapped the conversion functionality
• Updated class documentation to accurately reflect the current purpose of JSNodeMapper (mapping JSON structures to virtual JCR nodes for React's <Render> component)
• Applied consistent code formatting improvements (line wrapping)

Reviewed changes

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

File	Description
javascript-modules-engine-java/src/main/java/org/jahia/modules/javascript/modules/engine/jsengine/JSNodeMapper.java	Removed 3 unused methods related to JCR-to-JS conversion, updated documentation, and improved formatting
javascript-modules-engine-java/src/main/java/org/jahia/modules/javascript/modules/engine/js/server/RenderHelper.java	Removed unused transformToJsNode method that was a wrapper for the deleted functionality

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[dgriffon]

Looks good to me!
We need to be sure to remove them in a major version to avoid breaking change though

[GauBen]

This is not part of the documented API, we can safely remove it as "legacy implementation detail"

We can always revert the deletion in case this assumption is wrong