chore(aws-cdk-lib): npmignore source map files in v2 (#20363)

Closes #20320.

Our source maps do not work as expected when debugging on the downloaded `aws-cdk-lib` package. They are, however, useful when debugging locally. Since our goal is to reduce module size, this PR adds `*.map` to `.npmignore` so that the source maps are not packaged along with the rest of the files. 

From the results of `npm pack`:
- Before this change, the unpacked tarball size was 175.3 MB.
- After this change, the unpacked tarball size is 123.5 MB.

----

### All Submissions:

* [ ] Have you followed the guidelines in our [Contributing guide?](https://github.com/aws/aws-cdk/blob/master/CONTRIBUTING.md)

### Adding new Unconventional Dependencies:

* [ ] This PR adds new unconventional dependencies following the process described [here](https://github.com/aws/aws-cdk/blob/master/CONTRIBUTING.md/#adding-new-unconventional-dependencies)

### New Features

* [ ] Have you added the new feature to an [integration test](https://github.com/aws/aws-cdk/blob/master/INTEGRATION_TESTS.md)?
	* [ ] Did you use `yarn integ` to deploy the infrastructure and generate the snapshot (i.e. `yarn integ` without `--dry-run`)?

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

Author: kaizencc

Diff for: packages/aws-cdk-lib/.npmignore

@@ -27,3 +27,6 @@ tsconfig.json
 junit.xml
 
 !*.lit.ts
+
+# exclude source maps as they only work locally
+*.map

Diff for: packages/aws-cdk-lib/scripts/minify-sources.sh

@@ -16,4 +16,12 @@
 scriptdir=$(cd $(dirname $0) && pwd)
 cd ${scriptdir}/..
 
-find . -name '*.js' ! -name '.eslintrc.js' ! -path '*node_modules*' | xargs npx esbuild --sourcemap --platform=node --format=cjs --minify-whitespace --minify-syntax --tsconfig=tsconfig.json --allow-overwrite --outdir=.
+find . -name '*.js' ! -name '.eslintrc.js' ! -path '*node_modules*' | xargs npx esbuild \
+  --sourcemap \
+  --platform=node \
+  --format=cjs \
+  --minify-whitespace \
+  --minify-syntax \
+  --tsconfig=tsconfig.json \
+  --allow-overwrite \
+  --outdir=.