Enable to get build definition from Inspect API

This commit adds two fields to the response of Inspect API.

- Definition: Build definition of the first build executed by Build API.
- CurrentDefinition: Build definition of the latest build executed by Build or
  Solve API.

The client can use these information for debugging the build deeply.

Signed-off-by: Kohei Tokunaga <ktokunaga.mail@gmail.com>

controller/local/controller.go

@@ -146,7 +146,15 @@ func (b *localController) Inspect(ctx context.Context, ref string) (*controllera
 	if ref != b.ref {
 		return nil, errors.Errorf("unknown ref %q", ref)
 	}
-	return &controllerapi.InspectResponse{Options: b.buildConfig.buildOptions}, nil
+	var curDef *solverpb.Definition
+	var origDef *solverpb.Definition
+	if b.buildConfig.resultCtx != nil {
+		curDef, _ = build.DefinitionFromResultHandler(ctx, b.buildConfig.resultCtx)
+	}
+	if b.originalResult != nil {
+		origDef, _ = build.DefinitionFromResultHandler(ctx, b.originalResult)
+	}
+	return &controllerapi.InspectResponse{Options: b.buildConfig.buildOptions, Definition: origDef, CurrentDefinition: curDef}, nil
 }
 
 func (b *localController) Solve(ctx context.Context, ref string, target *solverpb.Definition, progress progress.Writer) error {