Test against loopy::kernel_callables_v3-edit2 (#88)

* bessel function mangling -> BesselFunction: ScalarCallable

* query translation unit's default_entrypoint's args

* [drop before merge]: test with kcv3-e2

* Add transfer_requirements_git_urls from grudge to downstream projects

* Point requirements.txt for loopy back to main

Co-authored-by: Andreas Klöckner <inform@tiker.net>