fix(dia.HighlighterView): prevent highlighting nodes outside cell view

[kumilingus]

Description

When a highlighter is used with an SVGElement as its NodeSelector, and that element is not part of the CellView, the node will not be highlighted. Instead, a cell:highlighter:invalid event is triggered—similar to what happens with a non-existent selector.

Motivation and Context

When a port is highlighted using an SVGElement selector and its attributes are updated, we need to make the highlighter invalid. This is because ports are re-rendered on each update, and the original SVGElement is removed from the DOM. The problem manifest during link reconnection, when the use set port attributes on link:connect event.

Note: This issue does not occur when using a JSON-based selector.

[Copilot]

Pull Request Overview

This PR improves the HighlighterView behavior by ensuring that highlighting only applies to nodes within the cell view.

• Updated tests verify that nodes outside the DOM are not highlighted.
• Modified the HighlighterView implementation to include a check using cellView.el.contains.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
packages/joint-core/test/jointjs/dia/HighlighterView.js	Adjusted test assertions to confirm the update behavior when nodes are detached from the DOM and the handling of the dirty flag.
packages/joint-core/src/dia/HighlighterView.mjs	Added a condition to ensure that a node is only highlighted if it is a valid SVGElement within the cell view.