[ORC] Add "wrap" and "unwrap" steps to ExecutorAddr toPtr/fromPtr.

The wrap/unwrap operations are applied to pointers after/before conversion to/from
raw addresses. They can be used to tag, untag, sign, or strip signing from
pointers. They currently default to 'rawPtr' (identity) on all platforms, but it
is expected that the default will be set based on the host architecture, e.g.
they would default to signing/stripping for arm64e.