Forbid explicit `any`, migrate to `unknown` or proper typing

[krassowski]

References

https://github.com/jupyterlab/jupyterlab/issues/16038

Code changes

Forbids any, except in variadics.

The intent is to:

• keep any in core APIs to avoid disruption (just add eslint-disable comments as needed)
• use unknown in leaf APIs and in function bodies where we can be fairly certain it will not cause disruption

TODO:

• [x] this PR and this rule should not apply to test files to reduce the diff and because we worry less about typing in tests

User-facing changes

None

Backwards-incompatible changes

TBD

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