Expose perfetto start and stop sessions

Modified the existing tests to use the APIs instead of
including a separate test native library for this.

The tests also utilize the in-process backend which makes
it a lot easier to verify trace events.

Test: atest PerfettoTraceTest
Bug: 303199244
Flag: android.os.perfetto_sdk_tracing_v2
Change-Id: If3c638a588ef6fe3d9e52728b6be74481c7a2a35