chore: update license headers to use shorter SPDX header

[miketheman]

Instead of the longer license header, replace with a shorter SPDX version.

Refs: https://spdx.dev/learn/handling-license-info/

[miketheman]

I'm considering that this might be a good idea to split out part of this PR to separate PRs so that we can use the .git-blame-ignore-revs feature to remove the change from a normal git blame.

If you do think it's a good idea, I'd split out to two PRs:

• the license checker and docs change
• all the remaining license header changes, including translations

Once merged & deployed, a third PR to add a .git-blame-ignore-revs file with the commit hash of the actual license header changes.

I don't feel strongly about this, but wanted to surface the ability in case that was a concern.

[miketheman]

CodeQL failures are due to touching files, and thus scanning "changed" files, so nothing is actually new here.

[ewdurbin]

I'm:

• +1 to the outcome/intent.
• NULL on the actual implications of this from a licensing concern (this document says it's fine/sufficient but I am not an expert).
• +1 to including handling of .git-blame-ignore-revs to keep this from cluttering blame history

[ewdurbin]

I say go for it, but with git blame ignore handling.

[miketheman]

Excellent! Converting back to draft to split apart and ship parts to accomplish the git blame ignore

[miketheman]

Closing now that the deed is done, and the ignore is part of #18219