trace2: add macOS process ancestry tracing

trace2: add macOS process ancestry tracing

In 353d3d77f4 (trace2: collect Windows-specific process information,
2019-02-22) Windows-specific process ancestry information was added as
a data_json event to TRACE2. Furthermore in 2f732bf15e (tr2: log
parent process name, 2021-07-21) similar functionality was added for
Linux-based systems, using procfs.

Teach Git to also log process ancestry on macOS using the sysctl with
KERN_PROC to get process information (PPID and process name).
Like the Linux implementation, we use the cmd_ancestry TRACE2 event
rather than using a data_json event and creating another custom data
point.

Signed-off-by: Matthew John Cheetham <mjcheetham@outlook.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>