Improve accuracy of Frontend packages, events documentation

[aduth]

🛠 Summary of changes

Updates the Frontend Architecture documentation to improve a few inaccuracies:

• We don't require listing sibling package dependencies between Yarn workspace packages
• private must be specified in all package.json (enforced by scripts/validate-workspaces.js), not just for published packages
• Generalize the recommendation around what was intended with the index.js documentation, also using the recommended TypeScript file extension, and allowing equivalent exports or main
• Describe JavaScript package integration using ViewComponents, which is generally preferable to packs
• Describe ALLOWED_EVENTS accurately as an allowlist, rather than a mapping

📜 Testing Plan

Verify that documentation revisions are sensible.

[zachmargolis]

does this URL need to point at the actual file?

Suggested change

	This is an allowlist of events defined in [AnalyticsEvents][analytics_events.rb] which are allowed
	This is an allowlist of events defined in [AnalyticsEvents][../app/services/analytics_events.rb] which are allowed

[aduth]

This comment is making me realize that the way I went about this is prone to causing confusion, but these are using reference links, defined at the end of the heading section:

identity-idp/docs/frontend.md

Lines 152 to 153 in c7fa569

	[frontend_log_controller.rb]: https://github.com/18F/identity-idp/blob/main/app/controllers/frontend_log_controller.rb
	[analytics_events.rb]: https://github.com/18F/identity-idp/blob/main/app/services/analytics_events.rb

[zachmargolis]

same: fix path?

Suggested change

	Any event logged from the frontend must be added to the `ALLOWED_EVENTS` allowlist in [`FrontendLogController`][frontend_log_controller.rb].
	Any event logged from the frontend must be added to the `ALLOWED_EVENTS` allowlist in [`FrontendLogController`][../app/controllers/frontend_log_controller.rb].