[webgpu][headers] Updates generated FreeMembers functions to match upstream.

- Upstream header generates the FreeMembers functions as psuedo "methods"
  on the structs. This make ordering of procs typedefs and procs
  different than the ones in Dawn. This change makes it so that Dawn's
  generators now generate those functions the same way.
- A large portion of the changes in this is adding 'API` in front of
  API functions for the wire code. This was done for two reasons:
    1) It is more consistent with how native does things where the
       implementation of the API functions are prefixed so that its
       very obvious when scanning the headers.
    2) Since the wire is using the `RefCounted` common class along
       with the `RefCountedWithExternalCount` classes now, those
       classes assume that the API version of `AddRef` and
       `Release` are called with the API prefix. By doing this, it
       actually simplifies all the special handling we had in the
       generated code for these functions.
- Some fairly minor changes in the generators helpers was also made
  to facilitate the other changes.

Change-Id: Ibdfed8b21a1a41a42fadc45018e8b33f4ac052c4
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/247536
Commit-Queue: Loko Kung <lokokung@google.com>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>