Support async sections in TraceSectionMetric

Test: TraceSectionMetricTest
Relnote: N/A

Change-Id: Iafee9db80d6c08cad84d7a7c2ee0f31a02af18c9

• benchmark/benchmark-macro/src/androidTest/java/androidx/benchmark/macro/TraceSectionMetricTest.kt[diff]
• benchmark/benchmark-macro/src/main/java/androidx/benchmark/macro/Metric.kt[diff]
• benchmark/benchmark-macro/src/main/java/androidx/benchmark/macro/perfetto/PerfettoTraceProcessor.kt[diff]