Add proposal "Opening existential arguments to optional parameters" (#1799)
Add proposal "Opening existential arguments to optional parameters" (#1799)

* Add proposal "Opening existential arguments to optional parameters"

* Update 0375-opening-existential-optional.md

Co-authored-by: Xiaodi Wu <9d06c3622fd33dbb326b4a8468b678bf421c5d05@users.noreply.github.com>
apple/swift-evolution,apple/swift-evolution