Unfreeze_gently doesn't have to be a method of
frozen_mutation. It might as well be implemented as
a free function reading from a frozen_mutation
and preparing a mutation gently.
The logic will be used in a later patch
to make a canonical mutation directly from
a frozen_mutation instead of unfreezing it
and then converting it to a canonical_mutation.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>