is duplicated by:

• SR-3027 add Array.init(minimumCapacity: Int)

Issue Description:

When knowing an array will immediately be filled with a specific count of items it is often common to write:

var array = [Value]()
array.reserveCapacity(count)

it would be nice to have an initializer that reserves capacity (since it would be similar to other allocation paths of buffers)

var array = [Value](reservingCapacity: count)

trivially this could be written as:

extension Array {
    init(reservingCapacity count: Int) {
        self.init()
        self.reserveCapacity(count)
    }
}