feat(cx-api): graduate to stable 🚀 (#13859)

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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/cx-api/README.md

@@ -3,13 +3,7 @@
 
 ---
 
-![cdk-constructs: Experimental](https://img.shields.io/badge/cdk--constructs-experimental-important.svg?style=for-the-badge)
-
-> The APIs of higher level constructs in this module are experimental and under active development.
-> They are subject to non-backward compatible changes or removal in any future version. These are
-> not subject to the [Semantic Versioning](https://semver.org/) model and breaking changes will be
-> announced in the release notes. This means that while you may use them, you may need to update
-> your source code when upgrading to a newer version of this package.
+![cdk-constructs: Stable](https://img.shields.io/badge/cdk--constructs-stable-success.svg?style=for-the-badge)
 
 ---
 

packages/@aws-cdk/cx-api/package.json

@@ -88,8 +88,8 @@
   "engines": {
     "node": ">= 10.13.0 <13 || >=13.7.0"
   },
-  "stability": "experimental",
-  "maturity": "experimental",
+  "stability": "stable",
+  "maturity": "stable",
   "awslint": {
     "exclude": [
       "props-default-doc:@aws-cdk/cx-api.MetadataEntry.data",