chore: add missing copyright headers

[AaronO]

Complements #9909, cc @bartlomieju

Finding files with missing copyright headers

find . -name "*.rs" | grep -v "./target/" | xargs -I{} bash -c 'cat {} \
    | grep "// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license." \
    &>/dev/null || echo {}'

./runtime/ops/webgpu.rs
./op_crates/webgpu/error.rs

[bartlomieju]

Thanks!