Add perf metrics

[JoshLove-msft]

We should check in some perf timing metrics to track the perf of the generator over time. It could include summary statistics of repeated runs of the Sample-TypeSpec library generation. If we do check something in, it would need to be based on CI runs, not local.

[JoshLove-msft]

Even just writing the time it takes to generate might be a good step.

[JoshLove-msft]

The compiler has a statistics flag that we can use to collect metrics. #7377

We can include this flag in our generate script just so we can see the perf times.