Dumping core can happen at the end of a profiling run, and in that case
we have to protect the target process and take the lock while iterating
over its region map.
Fixes#4509.
And make an effort to propagate errors out from the inner parts.
This fixes an issue where the kernel would infinitely loop in coredump
generation if the TmpFS filled up.
LexicalPath is a big and heavy class that's really meant as a helper
for extracting parts of a path, not for storage or passing around.
Instead, pass paths around as strings and use LexicalPath locally
as needed.
When a process crashes, we generate a coredump file and write it in
/tmp/coredumps/.
The coredump file is an ELF file of type ET_CORE.
It contains a segment for every userspace memory region of the process,
and an additional PT_NOTE segment that contains the registers state for
each thread, and a additional data about memory regions
(e.g their name).
