[9.20] new: dev: Add MOVE_OWNERSHIP() macro for transferring pointer ownership

A helper macro that returns the current value of a pointer and sets
it to NULL in one expression, useful for transferring ownership in
designated initializers.

Backport of MR !11724

Merge branch 'backport-ondrej/TAKE_OWNERSHIP-macro-9.20' into 'bind-9.20'

See merge request isc-projects/bind9!11736