- Change dev profile settings. Improves build performance; will not affect anything else. Details below.
- Introduce script for benchmarking various incremental builds. Usage is explained in the script comments.
- Add a line to `intervals` showing total main-thread CPU work logged in a profile; this can be used to compare the results of optimizations (I'll be starting a discussion informed by that data separately; this change just enables the tooling to report it).
