Align callback error handling with other SDKs #6081

Description

Currently Java SDK does not follow the new spec for callbacks.
If an error happens in a customer callback (hook), the SDK should fall back according to spec.

Gaps in Java SDK:

• beforeBreadcrumb: on error the breadcrumb is added as is, it should be dropped instead
• eventProcessor: on error the event/telemetry goes further in the pipeline, it should be dropped instead

Client reports:

• there's a new discard reason callback_error (https://develop.sentry.dev/sdk/telemetry/client-reports/#discard-reasons-1) which should be used to make this distinguishable from things being filtered out on purpose.