Block Editors: avoid discard changes for no changes (Fixes #20680)

[nielslyngsoe]

Fixes #20680

Fixes cherry-picked from v.17

[Copilot]

Pull request overview

This PR fixes issue #20680 where block editors (Block List, Block Grid, and RTE with blocks) were prompting users to discard changes even when no actual changes were made. The root cause was that observable value updates were being triggered unnecessarily, causing the change detection system to incorrectly identify unsaved changes.

Key Changes:

• Imported and used jsonStringComparison utility to compare values before updating them
• Added early return checks when values are identical to prevent spurious change detection
• Applied the fix consistently across three block editor components

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/Umbraco.Web.UI.Client/src/packages/rte/components/rte-base.element.ts	Added value comparison checks in three locations within the observable callback to prevent unnecessary updates when layouts/content/settings haven't changed
src/Umbraco.Web.UI.Client/src/packages/block/block-list/property-editors/block-list-editor/property-editor-ui-block-list.element.ts	Added value comparison checks in two locations to prevent setting undefined when already undefined and to avoid updates when the new value matches the current value
src/Umbraco.Web.UI.Client/src/packages/block/block-grid/property-editors/block-grid-editor/property-editor-ui-block-grid.element.ts	Added value comparison checks in two locations, mirroring the block-list implementation for consistency