Add SoongExecutionMetrics to ninja run

This adds metrics for partial compilation to Soong.

- Soong_ui names the directory SOONG_METRICS_AGGREGATION_DIR, which it
  empties before each ninja run.
- Find_input_delta writes metrics there
- At the end of the build, Soong_ui aggregates the metrics that were
  written to generate the aggregated metrics.

Bug: b/376287012
Test: Manual, TH
Change-Id: I123df654f5b963fcd213b5c4d815173051f5d72e