This PR renames `ActionSlot::name` to `ActionSlot::identifier` for both DNA and
RNA, and also renames related methods, functions, constants, and comments.
The purpose of this rename is to help make it clear that this is not a "name"
in the traditional sense, but rather is a composite of the slot name + id type
for lookup purposes.
Ref: #130892
Pull Request: https://projects.blender.org/blender/blender/pulls/130740
c0fd193abf