feat: gen /lib & /types from /src & drop /dist (v6)

[ephys]

Closes #14038

This is a pretty big PR that changes how we build sequelize.
Hopefully this is the last post TS migration fix PR.

During the initial TS migration, /lib was changed from a pure JS folder to a mix of JS and TS. /dist/lib became the "new" /lib.
This already broke things so we told node to map /lib to /dist/lib using 'exports' in package.json.

We still had issues where users would sometimes manage to import their typings from /lib instead of /types so we deduplicated typings to ensure users would always import the right typing file.

This lead to a subsequent issue where, because files in /lib were typescript files and not typescript declaration files, typescript would complain if the code did not match how the user configured their tsconfig.json

So now, I'm opening a pretty drastic PR: The goal is to allow .d.ts to reference our new .ts files without having to publish any .ts file.

• /lib, /types have been merged together in /src
• /lib and /types are generated using yarn build. They contain respectively only pure JS and the ts declarations. This matches as closely as I could what we had before the TS migration.
• /dist is gone (which should be fine because it was already impossible to import directly due to exports in package.json. It had to be imported as "sequelize/lib")
• Only /lib, and /types folders are published to npm
• exports in package.json reflects the changes so imports should not be broken.

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This PR targets v6.

Unfortunately, this is going to break many/all PRs once added to main. :(
I'll open a PR to do the same in main once this one is merged.

[ephys]

I accidentally ran eslint on .d.ts files it looks like. I can revert those changes if you want. Especially since they go against the new lint config

Edit: i'll revert the changes that go against the current linter but keep the others - as I'll cherry pick this PR in main afterwards
Edit: done

[WikiRik]

Two small remarks but looks good. Too bad we can't really do a v6-beta release to let people test this out, so we'll just have to make a new release with this. Should we rename the PR to be a feature?

[sdepold]

Since I prefer src over lib anyway I'm a big fan if this change 😅

[sdepold]

Shouldn't we have the same in v7?

[ephys]

I plan on opening a follow up PR to cherry pick in main (which I assume we can easily merge in v7 too? I don't know the extend to which main and v7 differ). Starting with v6 felt safer for some reason

Should we rename the PR to be a feature?

@WikiRik I agree, making this semver-minor would be better

Too bad we can't really do a v6-beta release to let people test this out

I've actually managed to reproduce the reported issue in a project of mine. I'll double-check that it's gone.
It's still possible I've missed something and things could break if people import directly from /types. But at this point if we have another bug report for it, I think it's safer to tell them to not import from /types

Edit: Well look at that, my own code was importing things from a wildly incorrect place :/

Likely due to webstorm auto-importing incorrectly.

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I'll open a follow-up PR to the follow-up PR to block users from importing any other file than 'sequelize' and 'sequelize/package.json'

[sdepold]

Oh v7 is just a copy of main. So if we target main, we can eventually just merge it into v7

[ephys]

Here we go. I hope this is the end of this painful situation :/

[github-actions]

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