It is now possible to send next and continue as separate signals. When
executing a build, the debug adapter will divide the LLB graph into
regions. Each region corresponds to an uninterrupted chain of
instructions. It will also record which regions depend on which other
ones.
This determines the execution order and it also determines what the
stack traces look like.
When continue is used, we will attempt to evaluate the last leaf node
(the head). If we push next, we will determine which digest would be the
next one to be processed.
In the future, this will be used to also support breakpoints.
Signed-off-by: Jonathan A. Sternberg <jonathan.sternberg@docker.com>