* Add support for `cause:` argument to `Fiber#raise` and `Thread#raise`.

The implementation behaviour is consistent with `Kernel#raise` and
`Exception#initialize` methods, allowing the `cause:` argument to be
passed to `Fiber#raise` and `Thread#raise`. This change ensures that
the `cause:` argument is handled correctly, providing a more consistent
and expected behavior when raising exceptions in fibers and threads.

[Feature #21360]

* Shared specs for Fiber/Thread/Kernel raise.

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Co-authored-by: Samuel Williams <samuel.williams@shopify.com>

* Improve consistency of `Fiber.current.raise`.

This automatically choosess whether to use transfer on a transferring
fiber or resume on a yielding fiber.  If the fiber is resuming, it
raises a FiberError.