windows: Migrate to windows 1809 base

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