fix(types): deduplicate error typings

[ephys]

Pull Request Checklist

• [n/a] Have you added new tests to prevent regressions?
• Does npm run test or npm run test-DIALECT pass with this change (including linting)?
• [n/a] Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• Did you update the typescript typings accordingly (if applicable)?
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Description Of Change

Closes #14000, I hope

This PR deduplicates the typing definitions for Error classes, as types/lib/errors.d.ts wasn't removed and was shadowing lib/errors.
I also fixed issues detected in lib/errors once it wasn't shadowed anymore

[WikiRik]

Just to check, this is compatible with the v6 branch right?

[ephys]

It should be. I've aligned the new files with the old typing definitions. But I'll double check that everything that was exported, still is

[WikiRik]

I was mostly thinking about files that weren't converted to TS in the v6 branch but I haven't looked at your changes yet.

[ephys]

These files were converted to TS just before we stopped the migration for v6 :) https://github.com/sequelize/sequelize/tree/v6/lib/errors

[WikiRik]

Looks good!

[github-actions]

🎉 This PR is included in version 7.0.0-alpha.6 🎉

The release is available on:

• npm package (@release-v7 dist-tag)
• GitHub release

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