Allow empty array in `generateStaticParams`

[rogermparent]

This PR attempts to tweak Next's internal logic as little as is necessary to allow the generateStaticParams function to return an empty array. An e2e test has been added to catch regressions, but it relies on an ugly workaround: as output: export isn't quite handled in e2e tests we use an always-succeeding stub test to ensure the build works without using next start. It's possible an integration test would be more appropriate here, but the docs lightly discourage them so I figured this would be the best place to start.

Fixes #61213

[ijjk]

Allow CI Workflow Run

• [ ] approve CI run for commit: f66d7f1d47014c23fbdac07ce436191ec40aaa3e

Note: this should only be enabled once the PR is ready to go and can only be enabled by a maintainer

[gtg7784]

is it still under review?