Potential use-after-free of AttributesProcessor in metric storage after MeterProvider shutdown

[lalitb]

There is a potential use-after-free bug in the OpenTelemetry C++ SDK metrics implementation.

Problem:

• Metric storage class(SyncMetricStorage) store a raw pointer to the AttributesProcessor instance, which is owned by the associated View.

• The View (and its AttributesProcessor) is owned by the ViewRegistry, which is managed by the MeterContext and ultimately the MeterProvider.

• When the MeterProvider is shut down or destroyed, the ViewRegistry and its Views are deleted, invalidating the AttributesProcessor pointer inside any metric storage objects.

• If metric instruments are recorded after shutdown (especially from other threads, background tasks, or due to application logic errors), this leads to use-after-free, undefined behavior, and possible segmentation faults.