[ruby-core:112517] [Ruby master Feature#19453] Move `Fiber.current` into core.

Issue #19453 has been reported by ioquatix (Samuel Williams). ---------------------------------------- Feature #19453: Move `Fiber.current` into core. https://bugs.ruby-lang.org/issues/19453 * Author: ioquatix (Samuel Williams) * Status: Open * Priority: Normal * Assignee: ioquatix (Samuel Williams) ---------------------------------------- i.e. don't `require 'fiber'` to use `Fiber.current`. Are there other methods we should consider too? -- https://bugs.ruby-lang.org/