feat(node): Add abnormal session support for ANR

[timfish]

This PR:

• Adds the abnormal_mechanism property to session types
• Passes the latest session from main process to ANR process
• If ANR is triggered and there's an active session, send the abnormal session
• Adds a test to check for the session update

This PR makes no attempt to suppress further session updates from the main app process. How does Sentry backend treat conflicting session updates?

Ref: getsentry/sentry-electron#774

[AbhiPrasad]

How does Sentry backend treat conflicting session updates

After the session hits a terminal state it cannot be updated anymore, so I think we are fine.

[romtsn]

How does Sentry backend treat conflicting session updates

After the session hits a terminal state it cannot be updated anymore, so I think we are fine.

Sorry for chiming in, this is correct^, but this should be enforced client-side iirc. On the server we can't really do that, because we have aggregates and don't keep reference on a single session, so there's no way to know whether it was terminated already when a new update comes in.

We've already faced this on Android once, when were sending multiple Crashed updates for a single session which resulted in an incorrect crash-free rate.

[romtsn]

Also, note that it's currently hardcoded for android-only and behind a feature flag, we'd have to relax those conditions (maybe even remove the flag altogether, it's been out for almost a year, but need to check with @shruthilayaj)

[timfish]

I've modified this PR so the ANR child process now notifies the main process that an ANR has been triggered and we clear any session from the scope.

This is probably not completely foolproof since we may have lost contact with the main process.