[roll] Roll fuchsia [trace] Implement isolated Max RSS measurement using C++ helper

Add a dedicated C++ binary `process_monitor` to measure Max RSS.
This tool forks and executes the target command, using `wait4` to
capture resource usage (`ru_maxrss`).

We previously used GNU `time` for this purpose, but it is not available
in all build/test environments.

We cannot simply use `getrusage(RUSAGE_CHILDREN)` in the parent because
`maxrss` is a lifetime maximum and often inherits the parent's RSS
across fork (see https://b.corp.google.com/issues/7633913), making it
useless for measuring a smaller child process if the parent is large.
By using a small, dedicated C++ helper that starts fresh, we ensure
a clean baseline for RSS measurement.

The `process_monitor` binary is built as a host tool and integrated
into `trace_importing.py` via `convert_trace_file_to_json_rusage`.

Test: fx test //src/performance/lib/trace_processing/tests:trace_importing_test
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1454989
Original-Revision: db82d8bb768625c5e43f6748247986c747025c27
GitOrigin-RevId: 6f56cc906bdf9c428ed4c5228ae3d4583a31993c
Change-Id: I6bb3c543a5b6432cc69dd621793b40ca751a66a4