Add user_data versions of exit event and syscall filter event

Recently several of our tools have wanted a user_data parameter in the exit event and the syscall filter event.
The user_data is used for C++ to pass `this` and to avoid global state in general.
The solution would be to add them to drmgr, with a piority and user_data.
Presumably we'd also add the DO_NOT_USE defines: so a source compat breakage.

Xref i#5161