Done to more clearly define event data categories, in preparation for #3229.

Fix `tests/test_basic.py::test_event_processor_drop_records_client_report` so that the test is idempotent on failure. Previously, the test was only idempotent on success; if the test failed, it would cause many other unrelated tests to fail with it.

`capture_record_lost_event_calls` replaces the `capture_client_reports` fixture. The fixture records calls to `Transport.record_lost_event` by noting the arguments passed to each call.

This change is being introduced in preparation for #3244, which changes `Transport.record_lost_event`'s signature and behavior.

Make the `report["discarded_events"]` assertion logic (in `test_data_category_limits_reporting`) not rely on the ordering of events or any sorting logic. Done in preparation of #3244, where the sorting logic cannot be relied on anymore, since the same number of spans will be discarded as transactions.

…calls`

Replace custom `record_lost_event` call capturing logic in `test_sampling.py` with the `capture_record_lost_event_calls` Pytest fixture. This change will simplify implementation of #3244.

Also, update existing transport tests so they pass against the changes introduced in this commit.

Resolves #3229

  - Add test for `record_lost_event` method's new `quantity` parameter
  - Add test for `record_lost_event` when passed a transaction item