Moves builder/shell_parser and into its own subpackage at builder/shell since it
has no dependencies other than the standard library. This will make it
much easier to vendor for downstream libraries, without pulling all the
dependencies of builder/.
Fixes#36154
Signed-off-by: Matt Rickard <mrick@google.com>
This is a work base to introduce more features like build time
dockerfile optimisations, dependency analysis and parallel build, as
well as a first step to go from a dispatch-inline process to a
frontend+backend process.
Signed-off-by: Simon Ferquel <simon.ferquel@docker.com>
