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
diff --git a/ui/build/dumpvars.go b/ui/build/dumpvars.go
index 5df3a95..e0b2c08 100644
--- a/ui/build/dumpvars.go
+++ b/ui/build/dumpvars.go
@@ -273,6 +273,7 @@
 		"BUILD_BROKEN_USES_BUILD_SHARED_LIBRARY",
 		"BUILD_BROKEN_USES_BUILD_STATIC_JAVA_LIBRARY",
 		"BUILD_BROKEN_USES_BUILD_STATIC_LIBRARY",
+		"RELEASE_BUILD_EXECUTION_METRICS",
 	}, exportEnvVars...), BannerVars...)
 
 	makeVars, err := dumpMakeVars(ctx, config, config.Arguments(), allVars, true, "")