devel/perfetto: new port

thj@ and adrian@ did all of the underlying FreeBSD-specific
porting work and testing. I helped with creating the Ports
tree Makefile.

Co-authored-by: Tom Jones <thj@FreeBSD.org>
Co-authored-by: Adrian Chadd <adrian@FreeBSD.org>
Differential Revision: https://reviews.freebsd.org/D56762