🔥 GitHub PRs on cloudflare/workerd repo should publish built npm packages

[IgorMinar]

Similarly to how workers-sdk repo publishes built artifacts for each PR, workerd repo should do the same to make it easy to test before the PR is merged.

A great example of the DX in the workers-sdk repo can be found here: cloudflare/workers-sdk#5220 (comment)

There is a lot of prior art in workers-sdk repo that should make the implementation of this productivity boost easier:

• https://github.com/cloudflare/workers-sdk/tree/main/.github/workflows#create-pull-request-prerelease-create-pullrequest-prereleaseyml
• https://github.com/cloudflare/workers-sdk/blob/main/.github/workflows/create-pullrequest-prerelease.yml