multiprocessing: add SharedMemory.rename() -- shm_rename() FreeBSD support

[c9ed70e6-85ba-41dd-8968-859cb0429c8e]

BPO	46398
Nosy	@vstinner, @koobs, @devnexen
PRs	python/cpython#30621

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields: ```python assignee = None closed_at = None created_at = labels = ['type-feature'] title = 'posixshmem module shm_rename freebsd support.' updated_at = user = 'https://github.com/devnexen' ``` bugs.python.org fields: ```python activity = actor = 'devnexen' assignee = 'none' closed = False closed_date = None closer = None components = ['FreeBSD'] creation = creator = 'devnexen' dependencies = [] files = [] hgrepos = [] issue_num = 46398 keywords = [] message_count = 1.0 messages = ['410694'] nosy_count = 3.0 nosy_names = ['vstinner', 'koobs', 'devnexen'] pr_nums = ['30621'] priority = 'normal' resolution = None stage = None status = 'open' superseder = None type = 'enhancement' url = 'https://bugs.python.org/issue46398' versions = [] ```

[c9ed70e6-85ba-41dd-8968-859cb0429c8e]

• Adding shm_rename (from FreeBSD 13) to be able to move a shared memory block from one location to another.