`borrow` and `take` parameter ownership modifiers

[tera]

@Karl

url.pathComponents.insert(prefix, at: url.pathComponents.index(after: url.pathComponents.startIndex))
^^^^^^^^^^^^^^^^^^                    ^^^^^^^^^^^^^^^^^^              ^^^^^^^^^^^^^^^^^^

// vs

ref path = url.pathComponents
path.insert(prefix, at: path.index(after: path.startIndex))

Personally it won't even occur to me to need borrowing here. I'd add some sugar and convert that into:

url.pathComponents[insertAt: 1] = prefix // or
url.pathComponents[1, insert: true] = prefix

(here "1" is a short version of path.index(after: path.startIndex), and insertAt is a simple variant of a subscript that inserts instead of replacing.