Reading /proc/self/task/<pid>/maps is not remapped to the target

Seeing this in qemu-user 3.1.0

The code in is_proc_myself which supports remapping of /proc/self/maps and /proc/<pid>/maps does not support remapping of /proc/self/task/<pid>/maps or /proc/<pid>/task/<pid>/maps. Extending is_proc_myself to cover these cases causes the maps to be rewritten correctly.

These are useful in multithreaded programs to avoid freezing the entire program to capture the maps for a single tid.