Abstract `ProcThreadAttributeList` into its own struct

[michaelvanstraten]

As extensively discussed in issue #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