Parse init accessors.

[hborla]

This is the SwiftSyntax-side change to swiftlang/swift#66283. Add parsing for init accessors:

struct Wrapper<T> {
  var wrappedValue: T
}

struct S {
  private var _value: Wrapper<Int>
  var value: Int {
    init(newValue) initializes(_value) {
      self._value = Wrapper(wrappedValue: newValue)
    }

    get { _value.wrappedValue }
    set { _value.wrappedValue = newValue }
  }
}

[hborla]

@swift-ci please test

[hborla]

@swift-ci please test

[hborla]

@swift-ci please test

[xedin]

@swift-ci please test Windows platform

[ahoppen]

I’ve got a couple of post-merge comments for additional test cases / diagnostics.

The parsing pieces look good to me. I’ve got some opinions of how the node types and children should be named but I’ll try to put together a document around naming guidelines for these and will address my thoughts on the names once that’s finished.

[ahoppen]

Could you add a test case for the following? We should be offering a Fix-It to switch the positions of initializes(x) and accesses(y)

struct S {
  var value: Int {
    init accesses(y) initializes(x) {}
  }
}

---

Also I think the following tests would be useful

struct S {
  var value: Int {
    get accesses(y) {}
  }
}

struct S {
  var value: Int {
    init throws {}
  }
}