Update old links pointing to /docs/extensions and /docs/extensionAPI

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• Website: Offer redirects
• Website: Update sitemap.xml
• Update all links in vscode-docs
  • Migrate ContentID. See API topics missing ms.ContentId in header #2234
• Update links in vscode
• Update links in vsce [DO NOT MERGE] Update links. Part of Microsoft/vscode-docs#2165 vscode-vsce#313
• Update links in yeoman generator
• Update all links in samples [DO NOT MERGE] Update all links for Microsoft/vscode-docs#2165 vscode-extension-samples#130

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• Update links in JSON hovers JSON hover should point to new docs vscode#62675

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@mjbvz Please find a suitable redirect address for https://github.com/Microsoft/vscode/blob/f90f0a9e138b809081c45a93eb4e881078b0937f/src/vs/workbench/api/node/extHostApiCommands.ts#L226, and replace it in VS Code source.