Fix invalid source maps from terser-webpack-plugin

[ijjk]

This fixes a regression in our source map generating which got lost in the big diff from the src folder restructure in #44405

These invalid source maps broke plugins that attempted to leverage them like @sentry/nextjs which only attempts in a production environment https://github.com/getsentry/sentry-javascript/blob/15ec85bead77100413381be821f42841ae114f93/packages/nextjs/src/config/webpack.ts#L586

For a regression test in a follow-up we will need to investigate a production test fixture with @sentry/nextjs although this requires a DSN be configured.

This also ensures we setup unhandledRejection and uncaughtException listeners during build so that we have proper stack information when these occur and the process isn't left hanging.

This also moves the extensionAlias config from #44177 to an experimental config as it seems to cause conflicts with ESM packages that define exports in their package.json which can be considered a breaking change.

Bug

• Related issues linked using fixes #number
• Integration tests added
• Errors have a helpful link attached, see contributing.md

Fixes: #45419
x-ref: slack thread

[lforst]

Hi, I just stumbled across this PR - happy to see this fixed!

For a regression test in a follow-up we will need to investigate a production test fixture with @sentry/nextjs although this requires a DSN be configured.

This would be amazing. Feel free to just ping me if you need help with anything Sentry related!