Add Client Reports to the native SDK

[JoshuaMoelans]

These allow users to see stats about the events that never got to Sentry, caused by a multitude of reasons (e.g. breadcrumb buffer overflow, sample rate discarding, before_send filtering, internal errors, ...).

This feature is described in detail on the following develop docs page: https://develop.sentry.dev/sdk/telemetry/client-reports/

We can take inspiration from the Java/Android SDK https://github.com/getsentry/sentry-java/issues/1894 (or the other SDKs mentioned on the linked issue)

[JoshuaMoelans]

On top of the historical data we should collect, for the new Logs product we should also collect the following:

• SDK must count each dropped log.
• SDK must calculate the size of each dropped log.
• SDK must emit both values as client outcomes.
• precise byte counting is not required; an approximate size is sufficient because:
  • Dropped logs are not billable.
  • sufficient to provide a rough overview to users (count + approximate size)

We already have a TODO in our logs.c code.

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