Diagnosability enhacement for TiDB X

## Enhancement
To boost problem investigation efficiency for TiDB X, we need to enhance the diagnosability.
Currently, we would like to enhance diagnosability in two main aspects:
1. For known anomalies that may happen, we perform defensive checks. Examples are assertions, max_ts update validity checks, stale read ts checks.
2. For unknown anomaly, we need event traces to narrow down the problem area.