userdebug: support perfetto traces as a section in incident reports

This set of patches adds a way for the perfetto command line client to
save a trace to a hardcoded location,
/data/misc/perfetto-traces/incident-trace, and call into incidentd to
start a report, which will include said trace in a new section.

This is not a long-term solution, and is structured to minimize changes
to perfetto and incidentd. The latter is currently architected in a way
where it can only pull pre-defined information out of the system, so
we're resorting to persisting the intermediate results in a hardcoded
location.

This will introduce at most two more linked files at the same time.

Bug: 130543265
Tested: manually on blueline-userdebug
Change-Id: Iaaa312d2d9da73ca329807211227a8c7a049102c