sdk-core: use core client as event emitter, send reports from database via client

[perf2711]

This PR adds event support for client directly.

Client events

You can attach to before-skip, before-send, and after-send events on client instance:

const client = BacktraceClient.initialize({ ... });
client.on('after-send', (report, data, attachments, result) => { ... });

This is required for me to use in smoketests, so I know if after-send is executed after e.g. an exception is thrown.

Database events

BacktraceDatabase now emits events of it's own:

type BacktraceDatabaseEvents = {
    added: [record: BacktraceDatabaseRecord];
    removed: [record: BacktraceDatabaseRecord];
    'before-send': [record: BacktraceDatabaseRecord];
    'after-send': [
        record: BacktraceDatabaseRecord,
        result: BacktraceReportSubmissionResult<BacktraceSubmissionResponse>,
    ];
};

[konraddysput]

since this is the internal api, maybe we can drop the deprecated field once we update all SDKs?

[perf2711]

since this is the internal api, maybe we can drop the deprecated field once we update all SDKs?

It turned out that this was only used in sdk-core. I removed this altogether.