This changes the syntax for constructing structs and classes to explicitly
mention the fieldnames, similar to JavaScript object literals.
The fields still have to be listed in the same order as in the struct/class
declaration.
As in Javascript, {foo: foo} can be abbreviated as {foo}.

Example:

macro NewJSArray(implicit context: Context)(
    map: Map, elements: FixedArrayBase): JSArray {
  return new JSArray{
    map,
    properties_or_hash: kEmptyFixedArray,
    elements,
    length: elements.length
  };
}

Drive-by cleanup: Make struct and class constructors follow the same pattern
                  in the parser and the AST.

Bug: v8:9018 v8:7793
Change-Id: I22ff7f68270e4f406aa80731a709d41ea52f52bb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1551999Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Daniel Clifford <danno@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60622}