Extract a real core error from CoreCrashedError for the Sentry Reporter

[drew2a]

Before the 7.12.1 release we saw all the core errors that led to an actual core crash as CoreCrashedError.

Thanks to changes in the #7021 we are now able to see the real exception inside the Stacktrace field (see #7065 as an example).

But sentry still use CoreCrashedError as the type for the exception (see https://sentry.tribler.org/organizations/tribler/issues/1619).

It would be nice to extract the real exception from the Stacktrace field and use it as an exception that Tribler sends to the Sentry.

[drew2a]

This is an example of the desired Sentry Event:
https://sentry.tribler.org/organizations/tribler/issues/1747