Previously when creating a new generic struct, one had to explicitly provide all type arguments, e.g., for the generic struct

  struct Box<T: type> {
    const value: T;
  }

one would initialize a new box using

  const aSmi: Smi = ...;
  const box = Box<Smi> { value: aSmi };

With the additions in this CL the explicit type argument can be omitted. Type inference proceeds analogously to specialization of generic callables.

Additionally, this CL slightly refactors class and struct initialization, and make type inference more permissive in the presence of unsupported type constructors (concretely, union types and function types).

R=jgruber@chromium.org, tebbi@chromium.org

Change-Id: I529be5831a85d317d8caa6cb3a0ce398ad578c86
Bug: v8:7793
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1728617
Commit-Queue: Georg Schmid <gsps@google.com>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63036}