To speed up Linux CI builds, use a set of self-hosted Linux machines and
use them to run all slow CI steps for Linux: "tests", bundling and
nightly builds.

Also adds a set of dev icons as Linux bundling script required them for
`run-bundling`-tagged builds from regular PRs.
Same icons as for Preview were used, but, ideally, something different
could be created.

Release Notes:

- N/A