Feature request: Add type information from CTF for userspace providers (USDT and pid)

[ericwmackay]

Dtrace already has the ability to retrieve type information from CTF for kernel providers (like fbt). It would be great to have this power and flexibility for userspace providers like USDT and pid.

An example use case is for untangling complex struct types in either entry or return probe args[]. A function you're trying to trace may take a generic pointer as an argument, and your probe definition needs to cast the pointer to some complex struct in order to retrieve data from struct members. Defining these structs in Dtrace, and accessing the struct members, may be extremely difficult through other means such as including header files. Types may not be fully defined until compile time. The qemu project is a great example of code that fits this scenario.