ctf: Add definitions for CTFv3

These are based on definitions added to binutils' libctf. Specifically:

• Type IDs are now encoded in 32 bits rather than 16, changing the layout of ctf_type_t, ctf_array_t, ctf_member_t and ctf_lmember_t.
• Type info is encoded in 32 bits rather than 16. The type "kind" is extended from 5 bits to 6, and the type "vlen" is extended from 10 bits to 25.

The main upside is that we remove the current limit, imposed by CTFv2,
of 2^{15} distinct types in the main kernel executable. Other limits,
such as that on the number of elements in an enum, imposed by the vlen
limit, are also raised.

This change adds v2 and v3 flavours of macros and type definitions which
differ between the two versions. Compatibility is preserved for now by
having generic names refer to the v2 definitions, so, e.g., ctf_type_t
is still a v2 type.

No functional change intended.

Reviewed by: Domagoj Stolfa
MFC after: 1 month
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D34360