Licencing statements for Solana contributed files

[ksolana]

Should we continue to use the default?

// Copyright (c) The Diem Core Contributors
// Copyright (c) The Move Contributors
// SPDX-License-Identifier: Apache-2.0

What are the alternatives?

• Append another line, something like: "Copyright (c) The Solana Contributors"
• Only keep "Copyright (c) The Solana Contributors"

[ksolana]

We should add something like: https://github.com/solana-labs/solana/blob/master/Cargo.toml#L116

[brson]

The license headers are enforced by CI, probably in the xlint tool, so if we make any changes we'll need to change that tool or its configuration.

For the code to be upstreamable we probably need to be able to pass their upstream licensing lints. That may or may not be a concern, though I assume it would be desirable to upstream the code. And as long as we keep the apache license, it should be possible to change any header text here to "move contributors" in the event we do upstream some code.

It doesn't really matter to me exactly what party is credited in the header text. I am inclined to leave things as upstream prefers.

[ksolana]

TODO /me: Try adding 'Copyright (c) The Solana Contributors' and see if lint complains