[grpc] update to 1.68.0

[Tradias]

From what I can tell gRPC always called CMake's add_custom_command with DEPENDS files that do not exist. But in this release they changed their cmake_minimum_required from 3.13 to 3.16 which seems to make that fail. I added a patch to address that. Note that the file are missing because they come from git submodules.

I tested gRPC with the x64-windows triplet and ran all tests within asio-grpc

• Changes comply with the maintainer guide.
• SHA512s are updated for each updated download.
• The "supports" clause reflects platforms that may be fixed by this new version.
• Any fixed CI baseline entries are removed from that file.
• Any patches that are no longer applied are deleted from the port's directory.
• The version database is fixed by rerunning ./vcpkg x-add-version --all and committing the result.
• Only one version is added to each modified port's versions file.

[JonLiu1993]

Feature codegen tested successfully in the following triplet:

• x86-wdinwos
• x64-wdinwos
• x64-windows-static

[BillyONeal]

Thanks for the update!