Use iife when bundling browser apps

[sigma-andex]

Description of the change

TODO

Checklist:

• Added the change to the "Unreleased" section of the changelog
• Added some example of the new feature to the README
• Added a test for the contribution (if applicable)

P.S.: the above checks are not compulsory to get a change merged, so you may skip them. However, taking care of them will result in less work for the maintainers and will be much appreciated 😊

[CarstenKoenig]

Not sure how other folks like to use this but I like to add the global name option to wrap the exports into an object.
I think this is very close to the way purescript was bundled before and it's really helpful for me when I like to call main with arguments (a bit like Elm does with flags) or when I want to expose other functions/entry points into the app.

Maybe we could add a flag to use --global-name=PS or even let users choose the name?

[sigma-andex]

We had some discussions about the esbuild in the working group and I think the consent was that we didn't want to wrap the whole esbuild params list but just the basic parameters. I think a flag to add any additional esbuild params like --purs-args would make sense, but I guess that deserves a different issue/pr then.

[CarstenKoenig]

Ok I guess users can opt to directly use esbuild in this case - still very much appreciate this PR as it would get rid of an bug/error I had when using spago bundle-app without --minify when something exports document ❤️