Add --ninja_weight_source option

It has 3 options for now.
* ninja_log: uses ninja log file for data source
* evenly_distributed: pass empty list for ninja to consider every work as the same
* not_used: do not use critical path logic in ninja

In addition, I added the option in the metrics to track

Bug: 271527305
Test: m --ninja_weight_source=ninja_log|empty|not_used
Change-Id: Ib4c812c20606a34b17d3f0edb71057b477c4f90e