Add ScanChunk to allow injecting Chunks into the SourceManager's channel

With the introduction of the SourceManager, the chunks channel became
private and read-only. This provides a method to write chunks into the
channel as we transition away from needing to do that.

pkg/engine/engine.go

@@ -415,6 +415,13 @@ func (e *Engine) ResultsChan() chan detectors.ResultWithMetadata {
 	return e.results
 }
 
+// ScanChunk injects a chunk into the output stream of chunks to be scanned.
+// This method should rarely be used. TODO: Remove when dependencies no longer
+// rely on this functionality.
+func (e *Engine) ScanChunk(chunk *sources.Chunk) {
+	e.sourceManager.ScanChunk(chunk)
+}
+
 // detectableChunk is a decoded chunk that is ready to be scanned by its detector.
 type detectableChunk struct {
 	detector detectors.Detector

pkg/sources/source_manager.go

@@ -191,6 +191,13 @@ func (s *SourceManager) Wait() error {
 	return s.pool.Wait()
 }
 
+// ScanChunk injects a chunk into the output stream of chunks to be scanned.
+// This method should rarely be used. TODO: Remove when dependencies no longer
+// rely on this functionality.
+func (s *SourceManager) ScanChunk(chunk *Chunk) {
+	s.outputChunks <- chunk
+}
+
 // preflightChecks is a helper method to check the Manager or the context isn't
 // done and that the handle is valid.
 func (s *SourceManager) preflightChecks(ctx context.Context, handle handle) error {