Draft: [scout] SDK: Improve multiarch coverage
This moves various -dev packages from steamrt-libdevel-non-multiarch to steamrt-libdevel, focusing on those that seem to be related to the Steam client itself. Some have been updated with changes backported from later Debian releases to be multiarch co-installable, while others were already co-installable but had dependencies that were not.
steamrt/tasks#258
Depends on many MRs in the packaging namespace, for the packages that needed Multi-Arch changes backported.
/cc @denittis