chore: introduce pragma:context to cdk-integ (aws#15779)

Since context passed via command line overrides the App context, setting newStyleSynthesis in the pipeline integration tests will not work since in the v2 branch we set newStyleSynth to “false” explicitly in cdk-integ.

Introduce a new cdk-integ pragma that can be used to override this context and use it for pipelines integration tests.


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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/pipelines/test/integ.newpipeline.ts

@@ -1,5 +1,5 @@
 // eslint-disable-next-line import/no-extraneous-dependencies
-/// !cdk-integ PipelineStack
+/// !cdk-integ PipelineStack pragma:set-context:@aws-cdk/core:newStyleStackSynthesis=true
 import * as sqs from '@aws-cdk/aws-sqs';
 import { App, Stack, StackProps, Stage, StageProps } from '@aws-cdk/core';
 import { Construct } from 'constructs';

packages/@aws-cdk/pipelines/test/integ.pipeline-security.ts

@@ -1,4 +1,4 @@
-/// !cdk-integ PipelineSecurityStack
+/// !cdk-integ PipelineSecurityStack pragma:set-context:@aws-cdk/core:newStyleStackSynthesis=true
 import * as codepipeline from '@aws-cdk/aws-codepipeline';
 import * as codepipeline_actions from '@aws-cdk/aws-codepipeline-actions';
 import * as iam from '@aws-cdk/aws-iam';

tools/cdk-integ-tools/lib/integ-helpers.ts

@@ -8,6 +8,7 @@ const CDK_OUTDIR = 'cdk-integ.out';
 
 const CDK_INTEG_STACK_PRAGMA = '/// !cdk-integ';
 const PRAGMA_PREFIX = 'pragma:';
+const SET_CONTEXT_PRAGMA_PREFIX = 'pragma:set-context:';
 
 export class IntegrationTests {
   constructor(private readonly directory: string) {
@@ -95,10 +96,23 @@ export class IntegrationTest {
    * Return the "main" template or a concatenation of all listed templates in the pragma
    */
   public async cdkSynthFast(options: SynthOptions = {}): Promise<any> {
-    const context = {
+    const context: Record<string, string> = {
       ...options.context,
     };
 
+    // apply context from set-context pragma
+    // usage: pragma:set-context:key=value
+    const ctxPragmas = (await this.pragmas()).filter(p => p.startsWith(SET_CONTEXT_PRAGMA_PREFIX));
+    for (const p of ctxPragmas) {
+      const instruction = p.substring(SET_CONTEXT_PRAGMA_PREFIX.length);
+      const [key, value] = instruction.split('=');
+      if (key == null || value == null) {
+        throw new Error(`invalid "set-context" pragma syntax. example: "pragma:set-context:@aws-cdk/core:newStyleStackSynthesis=true" got: ${p}`);
+      }
+
+      context[key] = value;
+    }
+
     try {
       await exec(['node', `${this.name}`], {
         cwd: this.directory,