Generator telemetry should include timings for each table transform

We have timing information for the overall generator driver run time and timing for the individual generator run time within a driver.

We report each table operation via the `NodeExtensions.LogTables` extension method, but don't record how long it took to execute.

We should update the extension method to take a timespan that represents how long the table operation took to execute. We should then update the `CodeAnalysisEventSource.NodeTransform` to take that timespan and report it via ETW.

We can expand the `GeneratorTimerExtensions` extension methods that we use for generator timing to have a similar pattern for the table operations.

When we don't perform a table operation because the table is all cached, we should report the time as zero.