oak_abi: Switch to Prost from protobuf-rust (project-oak#666)

* Replacing protobuf-rust generated names with prost generated names was done with the following script

replace(){
 find oak sdk examples -type f -name '*.rs' -exec sed -i "s/$1/$2/g" {} \;
}

replace 'OakStatus::OAK_STATUS_UNSPECIFIED'  'OakStatus::Unspecified'
replace 'OakStatus::OK' 'OakStatus::Ok'
replace ERR_BAD_HANDLE ErrBadHandle
replace ERR_INVALID_ARGS ErrInvalidArgs
replace ERR_CHANNEL_CLOSED ErrChannelClosed
replace ERR_BUFFER_TOO_SMALL ErrBufferTooSmall
replace ERR_HANDLE_SPACE_TOO_SMALL ErrHandleSpaceTooSmall
replace ERR_OUT_OF_RANGE ErrOutOfRange
replace ERR_INTERNAL ErrInternal
replace ERR_TERMINATED ErrTerminated
replace ERR_CHANNEL_EMPTY ErrChannelEmpty

replace NOT_READY NotReady
replace READ_READY ReadReady
replace INVALID_CHANNEL InvalidChannel
replace ORPHANED Orphaned