Auto merge of rust-lang#2784 - bryangarza:future-sizes-tests, r=RalfJung

Add tests for moving data across await point

This patch adds a few tests to assert the current behavior when passing data across an await point. This will help to test out an upcoming fix for the issue of arguments in async functions growing in size because of the generator upvar that is generated when we desugar the async function.

See rust-lang/rust#62958

Also relates to rust-lang/rust#107500

FYI `@oli-obk` `@pnkfelix`

Author: bors