[llubi] Map tags into provenances (#200236)
This patch adjusts https://github.com/llvm/llvm-project/pull/185977 to
generate tags for provenances (i.e., pointer components excluding
addresses), instead of memory objects. This allows us to distinguish
between `read_provenance` and `provenance`. See the original comment in
https://github.com/llvm/llvm-project/pull/185977#discussion_r3310861793.
Currently, tags are only generated for those pointer components
associated with a known memory object. We may need some special tags for
`capture(address)`-only pointers and the result of inttoptr (wildcard
provenance) in the future.
