chore: include basic workspace file with jest configuration (#27008)

The upcoming v6 of the [VSCode jest plugin](https://github.com/jest-community/vscode-jest#virtualfolders) allows us to configure our monorepo packages as virtual folders.

This makes the built-in Test Explorer work out of the box.

<img width="466" alt="image" src="https://github.com/aws/aws-cdk/assets/379814/b98b3736-4713-49d7-bec6-816f14816e73">

Using the workspace is entirely optional. It can also serve as an example configurations.
But it does give a space to add recommended/opinionated VSCode settings without compromising contributor's ability to change `.vscode/settings.json`.

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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*

Author: mrgrain

aws-cdk.code-workspace

@@ -0,0 +1,34 @@
+{
+  "folders": [{ "path": "." }],
+  "settings": {
+    "jest.jestCommandLine": "node_modules/.bin/jest",
+    "jest.autoRun": "off",
+    "jest.virtualFolders": [
+      { "name": "aws-cdk", "rootPath": "packages/aws-cdk" },
+      { "name": "aws-cdk-lib", "rootPath": "packages/aws-cdk-lib" },
+      {
+        "name": "cli-lib-alpha",
+        "rootPath": "packages/@aws-cdk/cli-lib-alpha"
+      },
+      {
+        "name": "custom-resource-handlers",
+        "rootPath": "packages/@aws-cdk/custom-resource-handlers"
+      },
+      {
+        "name": "integ-runner",
+        "rootPath": "packages/@aws-cdk/integ-runner"
+      },
+      {
+        "name": "integ-tests-alpha",
+        "rootPath": "packages/@aws-cdk/integ-tests-alpha"
+      },
+      {
+        "name": "sdk-v2-to-v3-adapter",
+        "rootPath": "packages/@aws-cdk/sdk-v2-to-v3-adapter"
+      }
+    ]
+  },
+  "extensions": {
+    "recommendations": ["dbaeumer.vscode-eslint", "Orta.vscode-jest"]
+  }
+}