Move crostini/CrostiniSharePath to guest_os/GuestOsSharePath

Code which is common to all VMs (crostini, pluginvm, etc) will
move to this package.

This CL is a refactor/move only.  No change to logic.

Bug: 979078
Change-Id: Ie61679bf4062f03946e69b08f94cef97d7077010
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1679635
Reviewed-by: Timothy Loh <[email protected]>
Reviewed-by: Nicholas Verne <[email protected]>
Reviewed-by: Dominic Battré <[email protected]>
Reviewed-by: Steven Bennetts <[email protected]>
Commit-Queue: Joel Hockey <[email protected]>
Cr-Commit-Position: refs/heads/master@{#673122}
28 files changed