Reuse timing metric collection logic between `--timings` and `-Zbuild-analysis`

[weihanglo]

Problem

cargo report timings is going to supercede the pre-existing cargo build --timings flag. The two parallel implementations that haven't yet fully shared the metric collection logic between them.

Possible solutions

We'd like to remove the old logic of how --timings collect metrics, and instead push relevent LogMessages t an in-memory queue, and after the build, we reuse code in cargo report timings to replay and generate the HTML report.

This is currently blocked on #16420.