fix(serverless): Adjust v6 Lambda layer hotfix for v7

[Lms24]

This PR adapts the hotfix for the Lambda layer creation introduced in 6.19.7 (in #4982) for v7.

More specifically, this PR

• ensures that the s/dist/cjs change is applied to the .npmignore files added in fix(serverless): Re-add missing modules in Node AWS Lambda Layer #4982 and to build-awslambda-layer.js
• adds or adjusts .npmignore files in all Sentry packages that are dependencies of @sentry/serverless
  • therefore, the unnecessary source, test or config files that previously bloated the lambda layer zip are no longer present
• improves the build-awslambda-layer.js script by
  • improving documentation
  • changing variable names to be more expressive
  • (as a result, the changes in the script seem bigger than they actually are)

ref: https://getsentry.atlassian.net/browse/WEB-871

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	18.12 KB (-10.06% 🔽)
@sentry/browser - ES5 CDN Bundle (minified)	56.96 KB (-11.85% 🔽)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	16.89 KB (-10.43% 🔽)
@sentry/browser - ES6 CDN Bundle (minified)	51.2 KB (-11.69% 🔽)
@sentry/browser - Webpack (gzipped + minified)	18.8 KB (-19.09% 🔽)
@sentry/browser - Webpack (minified)	60.98 KB (-25.38% 🔽)
@sentry/react - Webpack (gzipped + minified)	18.82 KB (-19.13% 🔽)
@sentry/nextjs Client - Webpack (gzipped + minified)	42.51 KB (-11.54% 🔽)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	23.89 KB (-8.4% 🔽)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	22.41 KB (-8.45% 🔽)

[lforst]

Still kinda want the lambda layer to just build its own bundles but this looks good in the meanwhile. Thanks for cleaning up that file!