feat(adapter-cloudflare): add metafile option and print bundle stats

[d3lm]

This PR adds a new metafile option to the Cloudflare adapter. The metafile can be useful if you wanna analyze the bundle size.

I also decided to print the size of the worker bundle which is pretty handy to see as part of the build output.

Fixes #12921

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[Rich-Harris]

Thank you, though this seems like a slightly unusual thing to add to one specific adapter, or even for that matter all adapters that just happen to use esbuild (and obviously it would be bad to duplicate the code to different adapters). Can you elaborate on why this is helpful? Feels like something that potentially belongs in the adapter API

[d3lm]

Can you elaborate on why this is helpful?

The stats itself were just helpful for me to keep an eye on the bundle size because I noticed that my bundle was pretty big and printing it as part of the build step allows for quicker feedback loops. I then started optimizing the bundle and removing dependencies which are client-only.

And for that, the metafile comes in handy because it allows you to analyze the bundle via https://esbuild.github.io/analyze.

I agree, that we may wanna add this to the adapter API instead if all adapters use esbuild. Otherwise, we'd be duplicating the code. Alternatively, we could have some util functions.