lisa._assets.kmodules.lisa.introspect_header: Support tracepoint vtables

FEATURE

Support tracepoint vtable types that refer to kernel private in their
getters, so that the generated C code from BTF only contains forward
declarations to those types rather than a full dump of them.

This allows getters to use public types, which could otherwise not be
dumped under their original names as it would conflict with the
definition available in public headers. Dumping them under a modified
name is possible but breaks CFI, as CFI check relies on each types
having the same name both on the caller and callee sides.