If the IDL provides a default value for a interface method parameter, then use that default value if no argument is provided.
Removes a bunch of std::optional<T>'s from the C++ interfaces, and simplifies binding implementations.
Also fix some defaults of buffer size from 0 to kWholeSize. This was partially done in an earlier CL, but it seems I missed a few.
Bug: dawn:1143
Change-Id: Ifc1bb29a5e7ead42dd015d2333c743165f2459a6
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/65663
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Austin Eng <enga@chromium.org>