When the builder loads a dockerfile, it does it by using the base name of the dockerfile path and only loads the innermost directory. This means that the source name we're looking for is the base name and not the full relative path. Update the set breakpoints functionality so it takes this into account. Fixes scenarios where DAP is used with a dockerfile nested in the context. Signed-off-by: Jonathan A. Sternberg <jonathan.sternberg@docker.com>