Support profiling of chrooted processes

[Jongy]

gProfiler makes wide use of /proc/pid/root to access files in the mount namespace of processes. If a process is chrooted, its /proc/pid/root behaves somewhat differently, breaking our usage. See my note from this py-spy PR:

My understanding is that /proc/pid/root points to the root as the process sees it, while /proc/pid/maps give us paths as WE see it. We (py-spy) are not chrooted when py-spy runs outside the chroot, so we need to strip the chroot from the /proc/pid/maps value. As a generalization, we always strip the path, which in most cases is just / if the process is not chrooted.

• [ ] Python: this affects py-spy which we'll need to upgrade after https://github.com/benfred/py-spy/pull/562.
• [ ] Ruby: I assume rbspy is affected as well and will require a similar fix.
• [ ] Java: async-profiler itself is not affected, but our driver for async-profiler (java.py) is.
• [ ] perf: I think will handle but we need to test if we care about this case.

Keywords: chrooted chroot