Rollup merge of #120844 - compiler-errors:async-di, r=oli-obk

Build DebugInfo for async closures

The test is pretty bare, because I don't really know how to write debuginfo tests. I'd like to land this first, and then flesh it out correctly one it's no longer ICEing on master (which breaks people's ability to test using async closures).

r? oli-obk cc `@rust-lang/wg-debugging` (if any of y'all want to help me write a more fleshed out async closures test)

Author: matthiaskrgr