Auto merge of rust-lang#123604 - michaelvanstraten:proc_thread_attribute_list, r=<try>

Abstract `ProcThreadAttributeList` into its own struct

As extensively discussed in issue rust-lang#114854, the current implementation of the unstable `windows_process_extensions_raw_attribute` features lacks support for passing a raw pointer.

This PR wants to explore the opportunity to abstract away the `ProcThreadAttributeList` into its own struct to for one improve safety and usability and secondly make it possible to maybe also use it to spawn new threads.

try-job: x86_64-mingw

Author: bors