Update Node.js developer setup documentation

[sean-mcmanus]

Summary

Updates the extension developer prerequisites from Node.js 16.x to Node.js 24.x, matching the version used by the GitHub compile-and-test workflows. The secondary extension-building guide now links to that canonical prerequisite instead of maintaining a separate Node.js version that could drift.

This follows up on the Node.js compatibility discussion in #14633. The related Node.js pins were also audited:

• GitHub compile/test workflows and custom actions consistently use Node.js 24.
• Azure packaging, publishing, component-governance, and localization pipelines consistently use Node.js 22, which remains supported by the current dependency graph and was intentionally introduced as a separate production baseline.
• TypeScript module: node16, @types/node, and Node.js runtime comments are module/type or VS Code extension-host compatibility settings, not developer build-tool version pins.

Validation: git diff --check, relative link target/anchor verification, and a repository documentation search confirming no stale Node.js 16 prerequisite remains.

This PR was investigated and created by Copilot with GPT 5.6 Sol (in VS Code). Any message starting with ✨ Copilot: was sent by Copilot.

[Copilot]

Pull request overview

Updates developer-facing documentation to align the extension’s local development prerequisites with the Node.js version used by the GitHub compile/test workflows, and reduces the chance of future drift by linking secondary docs to a single canonical prerequisite.

Changes:

• Updated the Extension developer prerequisite from Node.js 16.x to Node.js 24.x.
• Updated the “Building the Extension” guide to link to the canonical Node.js prerequisite section instead of stating its own requirement.

Reviewed changes

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

File	Description
Extension/readme.developer.md	Updates the required Node.js version for extension development to 24.x.
Documentation/Building the Extension.md	Replaces the generic Node install step with a link to the canonical required Node.js version section.

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