feat: remove global event processors

[Litarnus]

Removes the static global processors list in favour of event processors on Scopes. The direct replacement for it is using the global scope directly:

SentrySdk::getGlobalScope()->addEventProcessor(...);

The reason to remove this is that we already have event processors on Scopes, meaning that the static list is redundant.

This PR also introduces a small optimisation and correction: We would run event processors unconditionally for all events, including logs and metric events which use less data than error events. That means that for all those events, we would add data only to discard it while serialising. The event processors are now guarded by type and are only executed for errors and transactions