feat(codebuild): add webhook Filter Groups. (#2319)

Fixes #1842

Author: Kaixiang-AWS

packages/@aws-cdk/aws-codebuild/README.md

@@ -90,7 +90,10 @@ Example:
 const gitHubSource = new codebuild.GitHubSource({
   owner: 'awslabs',
   repo: 'aws-cdk',
-  webhook: true, // optional, default: false
+  webhook: true, // optional, default: true if `webhookFilteres` were provided, false otherwise
+  webhookFilters: [
+    codebuild.FilterGroup.inEventOf(codebuild.EventAction.PUSH).andBranchIs('master'),
+  ], // optional, by default all pushes and Pull Requests will trigger a build
 });
 ```
 
@@ -283,4 +286,4 @@ new Project(stack, 'MyProject', {
     securityGroups: [securityGroup],
     vpc: vpc
 });
-```
+```

packages/@aws-cdk/aws-codebuild/lib/project.ts

@@ -625,7 +625,7 @@ export class Project extends ProjectBase {
         throw new Error(`Badge is not supported for source type ${this.source.type}`);
       }
 
-      const sourceJson = this.source.toSourceJSON();
+      const sourceJson = this.source._toSourceJSON();
       if (typeof buildSpec === 'string') {
         return {
           ...sourceJson,
@@ -670,7 +670,7 @@ export class Project extends ProjectBase {
       timeoutInMinutes: props.timeout,
       secondarySources: new Token(() => this.renderSecondarySources()),
       secondaryArtifacts: new Token(() => this.renderSecondaryArtifacts()),
-      triggers: this.source.buildTriggers(),
+      triggers: this.source._buildTriggers(),
       vpcConfig: this.configureVpc(props),
     });
 
@@ -822,7 +822,7 @@ export class Project extends ProjectBase {
   private renderSecondarySources(): CfnProject.SourceProperty[] | undefined {
     return this._secondarySources.length === 0
       ? undefined
-      : this._secondarySources.map((secondarySource) => secondarySource.toSourceJSON());
+      : this._secondarySources.map((secondarySource) => secondarySource._toSourceJSON());
   }
 
   private renderSecondaryArtifacts(): CfnProject.ArtifactsProperty[] | undefined {
@@ -889,15 +889,15 @@ export class Project extends ProjectBase {
     if (props.artifacts) {
       return props.artifacts;
     }
-    if (this.source.toSourceJSON().type === CODEPIPELINE_TYPE) {
+    if (this.source._toSourceJSON().type === CODEPIPELINE_TYPE) {
       return new CodePipelineBuildArtifacts();
     } else {
       return new NoBuildArtifacts();
     }
   }
 
   private validateCodePipelineSettings(artifacts: BuildArtifacts) {
-    const sourceType = this.source.toSourceJSON().type;
+    const sourceType = this.source._toSourceJSON().type;
     const artifactsType = artifacts.toArtifactsJSON().type;
 
     if ((sourceType === CODEPIPELINE_TYPE || artifactsType === CODEPIPELINE_TYPE) &&