feat(fetch-proxy): add X-Forwarded-Port header

[mjackson]

This keeps X-Forwarded-Host aligned with the original request Host value while adding a separate X-Forwarded-Port header when xForwardedHeaders is enabled. This follows the shape used by node-http-proxy and avoids changing existing consumers that expect the port to remain in X-Forwarded-Host.

Supersedes #10762.

• Adds X-Forwarded-Port for proxied requests when xForwardedHeaders: true
• Preserves the current X-Forwarded-Host behavior by continuing to use url.host
• Uses explicit request ports when present and falls back to 80 or 443 for default HTTP/HTTPS ports

let proxy = createFetchProxy('https://backend.example', {
  xForwardedHeaders: true,
})

await proxy(new Request('http://shopify.com:8080/search'))
// X-Forwarded-Proto: http
// X-Forwarded-Host: shopify.com:8080
// X-Forwarded-Port: 8080

[github-actions]

Preview Build Available

A preview build has been created for this PR. You can install it using:

pnpm install "remix-run/remix#preview/pr-11265&path:packages/remix"

This preview build will be updated automatically as you push new commits.

[github-actions]

The preview branch preview/pr-11265 has been deleted now that this PR is merged/closed.