Feat: v3 Refactor

[timfish]

This PR refactors the Electron SDK into thin layers on top of the browser and node SDKs.
Electron functionality is added via optional integrations.

This PR:

• Completely refactors the entire SDK into thinner layers on top of the browser/node SDKs with all features as integrations
  • See tracking issue Electron SDK v3 Proposal #360 for details of all the new integrations.
  • CommonJs build now outputs into the root directory so @sentry/electron/main, @sentry/electron/preload and @sentry/electron/renderer work
  • Added package.json exports key so modern bundlers can find ESM output via sub-module imports
  • Preloads scripts are pre-bundled so they work in sandboxed renderers
• Default session tracking
  • Added session support to the transport
  • Default session integration (MainProcessSession) tracks the lifetime of the main process
• Works with BrowserTracing and transactions
• Improved tests
  • Re-added store endpoint to test server for testing sending from the browser SDK
  • Add session supports to test server
  • Added tests for sessions/transactions
  • Added a lot of extra checks to all tests

Other Considerations...

• The docs were already out-of-date but this will require almost a complete rewrite
• This will require some beta releases to get feedback and confirm I haven't broken anything

Closes:
#360, #356, #355, #352, #351, #268, #254, #91

[HazAT]

@timfish can we bring this to a resolution and maybe ship a beta release so users can start trying it out?

[timfish]

Fixes #249

[timfish]

I think this might be ready for a beta!

[AbhiPrasad]

Can we create a new GH issue that covers a brief migration guide for the beta? We can then start iterating on that.

We need to update changelog as well?

[AbhiPrasad]

We can do the changelog in another commit or include it here - up to you. Thanks for the migration guide.

I think we good to

[timfish]

I've still got a little bit left to add to the migration guide. I'll finish it off and add a link to the changelog in this PR.

[timfish]

Other than updating the changelog, these final changes change all integration constructor options from arguments into options objects. This improves readability and allows for additions and modifications later without introducing breaking changes.

For example:

new ElectronEvents(false);
// becomes
new ElectronEvents({ unresponsive: false })

[AbhiPrasad]

Last minute double check - we good to change the target from es5 to es6?

[timfish]

I suppose I could be relying on the e2e tests too much here! They pass with Electron v2 so assumed everything is ok but we don't actually test all SDK features in the e2e tests yet 🤔

These changes make the minimum supported Electron version v2 which was node v8.9.3 and Chrome v61.

Apparently node 6.4.0 included almost all of ES2015 apart from proper tail call optimisation: https://node.green/

Chrome has supported the same since v51:
https://caniuse.com/es6

A quick search suggests v8 still doesn't support tail call optimisation so ES6 was essentially fully supported at these points for all intents and purposes 🤷‍♂️

[timfish]

This completely passed me by but v8 decided not to ship tail call optimisation so never technically supported full ES6:
https://v8.dev/blog/modern-javascript?m=1#proper-tail-calls

This means "ES6" has been supported since Electron v1.3.7 which means we could have targeted it before when the minimum Electron version was v1.6.

[AbhiPrasad]

Ok gotcha. Do we need to write down the minimum version for electron somewhere then?

Also we can probably catch this quickly on a beta release if something goes wrong, so fine to bump this here.

[timfish]

Minimum Electron version has been bumped to v2 in the readme