simpleperf: add context_switch msg type in report_sample output.

When --trace-offcpu is used, simpleperf keeps context switch records
in perf.data, to help calculate off-cpu time period. This CL further
exports that info to cmd_report_sample.proto, in context_switch msg type.

Also add trace_offcpu in meta_info msg, to explicitly mark if a profile
is recorded with --trace-offcpu.

Bug: 38383695
Test: run simpleperf_unit_test
Change-Id: I10de23f883e8df3ff1380046cafc2daee658ca4e
4 files changed