The server_audit_timestamp_format %f specifier always rendered zero
microseconds. The server downcast the precise time to seconds before
passing it to audit plugins, and the plugin then re-fetched the time
itself at write time.
Pass the server's high-resolution time through the audit API instead:
- extend mysql_event_general with general_time_microseconds (added in
MYSQL_AUDIT_INTERFACE_VERSION 0x0304), keeping general_time in
seconds for backward compatibility
- the server_audit plugin uses event->general_time_microseconds for
query log entries instead of re-fetching the time at write time
Connection and table events carry no timestamp in the audit API, so the
plugin keeps taking the time at event time for those entries.
Replace the contention prone mysql_prlock_t with a simpler
rw-lock wrapper from InnoDB, and fix several potential
race conditions by making consistent use of lock_operations.
This will also omit any PERFORMANCE_SCHEMA instrumentation.
