[Fix] Implement platform specific URL format

[rrmistry]

Fixes #238886

TLDR: Test with below steps

1. Add a built-in extension in product.json for multi-platform extensions (e.g. ms-python.debugpy)
2. Build the extensions list using npm run gulp compile-extensions-build

---

Please see the description in the related issue for how to test this in the linked issue.

The issue was that marketplace links required a URL query parameter for multi-platform extensions or it fails with HTTP 404 status (e.g. ?targetPlatform=linux-x64).

This was missing in the current implementation for the build/lib/extensions.ts::fromMarketplace function.

Fixed this by checking the platforms list from the IExtensionDefinition interface (as used in product.json). If this platforms key is specified and current platform is in the provided list then add the necessary URL query parameter for the marketplace service.

This was tested by adding the below platforms in the product.json file:

{
    // ...
    "extensionsGallery": {
        "serviceUrl": "https://open-vsx.org/vscode/gallery",
        "itemUrl": "https://open-vsx.org/vscode/item",
        "resourceUrlTemplate": "https://open-vsx.org/api/{publisher}/{name}/{targetPlatform}/{version}/file/{path}"
    },
    "linkProtectionTrustedDomains": [
        "https://open-vsx.org"
    ],
    "builtInExtensions": [
        // ...
        {
            "name": "ms-python.debugpy",
            "version": "latest",
            "platforms": [      // <<<<<<
                "linux-x64",    // <<<<<<
                "linux-arm64"   // <<<<<<
            ],                  // <<<<<<
            "repo": "https://github.com/microsoft/vscode-python-debugger",
            "metadata": {
                "publisherId": {
                    "publisherName": "ms-vscode",
                    "displayName": "Microsoft",
                    "flags": "verified"
                },
                "publisherDisplayName": "Microsoft"
            }
        }
    ]
}

---

Related: #180525 / PR: #182072

[rrmistry]

Converting to draft as I see that now I need to also update build/lib/extensions.js from the TypeScript file.

Will need to find out how to do that first so I can make the necessary edits and update the PR again.

[rrmistry]

@microsoft-github-policy-service agree

[rrmistry]

Apologies @818Nawaf for delays but I had to see what is the best native way to update the javascript files under build/lib/ folder from my changes.

Eventually found the command:

npm run update-build-ts-version

This updated build/lib/extensions.js from build/lib/extensions.ts

Could you please re-approve the PR?

Thank you!