refactor (v10): Mirror non-JSX types to the 'preact' namespace

[rschristian]

Closes #4903
Non-breaking form of #4878

Duplicates our DOM types into a new dom.d.ts file (matching v11), exporting them under the Preact namespace (so you can do import type { HTMLAttributes } from 'preact';), but maintains back-compat . This will allow library authors to switch to the Preact namespace and keep compatibility with v10 & v11 going forward.

There's obviously some duplication here but unfortunately it's necessary -- turns out you can't label namespace aliases (i.e., export import ...) as deprecated. We need to keep the current types where they are so that users are warned they're using deprecated APIs.

[github-actions]

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[maxpatiiuk]

Hi
Do you know when this change will be available on npm for preact@10?

[rschristian]

Next time we cut a release, but when that happens is TBD. We don't schedule things.