ACL configuration context variables are inconsistently named as `actx`,
`ac`, or `aclconfctx`, which caused confusion during code reviews. This
commit renames all `cfg_aclconfctx_t` variables to `aclctx`, which is
short, consistent, and unambiguous.
Closes #5530
Merge branch '5530-rename-actx' into 'main'
See merge request isc-projects/bind9!11003