[api/logs] Return NoopLogRecord from NoopLogger

[yurishkuro]

Fixes #2656

Changes

NoopLogger was incorrectly returning nullptr, causing segfaults in client code. After this change it returns a dummy no-op log record.

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[marcalff]

Thanks for the PR.

The idea to share a pointer on a dummy noop record, to avoid new + delete, unfortunately does not work, and causes the runtime failures seen in CI.

When logging 2 events in a row:

• CreateLogRecord() for event 1 returns a dummy record
• Delete log_record for event 1 calls the destructor, which invalidates the dummy record virtual table
• CreateLogRecord() for event 2 returns a damaged dummy record
• record->SetXXX() crashes when invoking virtual methods.

Implementing operator new() and operator delete() instead only moves the problem elsewhere, because the same crash will happen when 2 threads use the same dummy record concurrently.

[yurishkuro]

@marcalff then I suggest going back to allocating a new Noop record, that at least prevents the existing behavior that returns nullptr unexpectedly, and address performance issue separately.