fix(codepipeline): mark crossRegionReplicationBuckets and crossRegionSupport as experimental. (#3226)

BREAKING CHANGE: codepipeline.Pipeline.crossRegionReplicationBuckets is now experimental
* codepipeline.Pipeline.crossRegionSupport is now experimental
* codepipeline.CrossRegionSupport is now experimental

Author: skinny85

packages/@aws-cdk/aws-codepipeline/lib/pipeline.ts

@@ -88,6 +88,7 @@ export interface PipelineProps {
    * the construct will automatically create a Stack containing an S3 Bucket in that region.
    *
    * @default - None.
+   * @experimental
    */
   readonly crossRegionReplicationBuckets?: { [region: string]: s3.IBucket };
 
@@ -292,6 +293,8 @@ export class Pipeline extends PipelineBase {
   /**
    * Returns all of the {@link CrossRegionSupportStack}s that were generated automatically
    * when dealing with Actions that reside in a different region than the Pipeline itself.
+   *
+   * @experimental
    */
   public get crossRegionSupport(): { [region: string]: CrossRegionSupport } {
     const ret: { [region: string]: CrossRegionSupport }  = {};
@@ -617,6 +620,8 @@ export class Pipeline extends PipelineBase {
  * An interface representing resources generated in order to support
  * the cross-region capabilities of CodePipeline.
  * You get instances of this interface from the {@link Pipeline#crossRegionSupport} property.
+ *
+ * @experimental
  */
 export interface CrossRegionSupport {
   /**