Rename time to event in Soong metrics system.

Several structs and files are named time which records the total
execution of a traceable event. Soon, resource information of an
executed process is collected during a build event so a more generic
name is applied.

Bug: b/169453825
Test: go test and m nothing. Checked the soong_metrics protobuf.
Change-Id: I65a782603530d51018d6cc1192c18cfeef7566a0

ui/metrics/metrics.go

@@ -36,14 +36,14 @@ const (
 )
 
 type Metrics struct {
-	metrics    soong_metrics_proto.MetricsBase
-	TimeTracer TimeTracer
+	metrics     soong_metrics_proto.MetricsBase
+	EventTracer EventTracer
 }
 
 func New() (metrics *Metrics) {
 	m := &Metrics{
-		metrics:    soong_metrics_proto.MetricsBase{},
-		TimeTracer: &timeTracerImpl{},
+		metrics:     soong_metrics_proto.MetricsBase{},
+		EventTracer: &eventTracerImpl{},
 	}
 	return m
 }