Fix unhandled exception not captured when hub disabled

[mattjohnsonpint]

I noticed that the Sentry.Samples.Console.Basic example wasn't working when run on my Mac with the net48 target, but was working fine with the net6.0 target, or on Windows with either target.

After some investigation, it turns out that the Mono desktop runtime will call any Dispose from a using statement (or any finally block) before it invokes AppDomain.UnhandledException or similar events. That's probably a bug in Mono, as the behavior on .NET or .NET Framework is to fire those events immediately and not dispose. This doesn't look like it will be fixed in Mono any time soon, so we should accept the current behavior.

The problem is that if Hub.Dispose is called before the unhandled exception integration captures the exception, the hub will have been disabled and the exception won't be captured. The solution thus is to allow the unhandled exception integration (and similar) to capture even if the hub has been disabled.

While resolving this, I also noticed that we were checking IsEnabled only on extension methods like CaptureException, CaptureMessage, etc. So it was always possible to still send events post-dispose by calling CaptureEvent directly. That is a separate bug, but also resolved in this PR. The hub now checks if it is disabled before capturing anything, rather than the extension methods. An internal CaptureEventInternal and some related code will allow the integrations to bypass those checks and still capture on disabled hubs.

This change means that no events will not be captured post-dispose unless they come from an internal integration. That was always the intention, but only behaved that way with extension methods like CaptureException, and not with the basic CaptureEvent method.

[bitsandfoxes]

Does that mean that if the SDK got initialized it'll always capture Unhandled Exceptions even if it has been closed on purpose?

[mattjohnsonpint]

Does that mean that if the SDK got initialized it'll always capture Unhandled Exceptions even if it has been closed on purpose?

Yes. An unhandled exception leads to a crash, so we want to always catch those.

[bitsandfoxes]

LGTM!

[mattjohnsonpint]

This had the side effect of fixing #321 for exceptions. #2319 fixes it for transactions as well. 🎉