[cpp] Refactors callback info handling in cpp header.

- This refactor adds new utilities to unify callback info handling in
  the cpp header. This change only updates the methods that return a
  wgpu::Future, but in follow ups, we will also unify the generator to
  use the helpers for structs that have callback info members, i.e.
  the DeviceDescriptor.
- The refactor also introduces the concept of CArgConverter, which
  will allow us to extend the C++ API to handle more types of
  callbacks. The extensibility of this design will allow us to manually
  implement conversions when they are not trivial, i.e. the DeviceLost
  and UncapturedError callbacks will use this in a follow up. This
  will also allow us to provide callbacks that are more C++ friendly,
  i.e. the DawnCacheDeviceDescriptor and it's callbacks could be
  updated to be more like the one's in the DeviceDescriptor, and in
  C++, we can wrap the raw pointers in those callbacks with a
  std::span to provide additional safety.
- This change also implicitly removes support for the old char* types
  for messages in callbacks, and instead only supports
  wgpu::StringView for those. In another follow up, we could actually
  use the CArgConverter design to support std::string_view directly
  and potentially remove the wgpu::StringView type from the C++
  bindings entirely.

Bug: 512880446
Change-Id: I9ff6932b0dff92b41344b89a1c592495d7a60e0b
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/305676
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Loko Kung <lokokung@google.com>