chore(toolkit): publish alphas with version hash (#33256)

Make the local-publish helper include an identifiable build in the package version.
Also export `package.json` as this is good practice.

### Describe any new or updated permissions being added

n/a

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

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

Author: mrgrain

packages/@aws-cdk/toolkit/build-tools/package.sh

@@ -2,14 +2,17 @@
 
 version=${1:-latest}
 reset=0.0.0
+commit=$(git rev-parse --short HEAD)
 
 # Toolkit package root
 cd "$(dirname $(dirname "$0"))"
 
+npm pkg set version=0.0.0-alpha.$commit
 npm pkg set dependencies.@aws-cdk/cx-api=$version
 npm pkg set dependencies.@aws-cdk/cloudformation-diff=$version
 npm pkg set dependencies.@aws-cdk/region-info=$version
 yarn package --private
+npm pkg set version=$reset
 npm pkg set dependencies.@aws-cdk/cx-api=$reset
 npm pkg set dependencies.@aws-cdk/cloudformation-diff=$reset
 npm pkg set dependencies.@aws-cdk/region-info=$reset

packages/@aws-cdk/toolkit/package.json

@@ -10,7 +10,8 @@
     ".": {
       "types": "./lib/index.d.ts",
       "default": "./lib/index.js"
-    }
+    },
+    "./package.json": "./package.json"
   },
   "scripts": {
     "awslint": "cdk-awslint",