In order to support UTF-8 compatible filenames, keep the path representation of trace files as long as possible. When transmitting them as CBOR convert them using `u8string` function.
Also use non throwing overloads of some `std::filesystem` functions to avoid crashing the server if a file is deleted before a file operation is performed.
#jira UE-155288, UE-151250
#robomerge EngineMerge
#preflight 62bedb6bb447118888501429
[CL 20912946 by Johan Berg in ue5-main branch]