windows: Migrate to windows 1809 base
Rebuild the windows docker image against the current ltsc [1] of server 2019. This requires moving some of the msys setup to the runner job cause it causes docker build to hang
Switch the job tags so they now use the 1809 runner, instead of 1607.
Tweak the PATHs in the msys job so bash doesn't complain about slashes..
Lastly, increase the timeout of the windows jobs, as msys2 installs its deps at runtime
[1] https://docs.microsoft.com/en-us/windows-server/get-started-19/servicing-channels-19