RFC 68: Mandatory FFI declarations

[ergl]

Changes related to the implementation of RFC 68.

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Opening the PR now although it's not ready, to ask for feedback, etc

Tasks:

• Add FFI declarations for all Pony libraries under the ponylang org
• Add FFI declarations to the standard library and tests
• Remove FFI call return type declaration syntax
• Update tutorial

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This closes #3735

[ponylang-main]

Hi @ergl,

The changelog - changed label was added to this pull request; all PRs with a changelog label need to have release notes included as part of the PR. If you haven't added release notes already, please do.

Release notes are added by creating a uniquely named file in the .release-notes directory. We suggest you call the file 3739.md to match the number of this pull request.

The basic format of the release notes (using markdown) should be:

## Title

End user description of changes, why it's important,
problems it solves etc.

If a breaking change, make sure to include 1 or more
examples what code would look like prior to this change
and how to update it to work after this change.

Thanks.

[SeanTAllen]

Release notes for this should be pretty detailed with examples of code that was previously valid and how to fix it to make it valid after the change. If there are any tricky bits, those should be highlighted.

[ergl]

Okay, I think all the changes in the compiler are done. I know the diff is quite large, since there are a lot of declarations going on. Probably the most important things I'd like some review on would be the last two commits, where I enforce that FFI declarations exists, and where I remove the syntax for specifying the return type on FFI calls.

[ergl]

The CI errors are due to the test-validate-grammar step. I don't have a good idea on how to update the pony.g file to reflect the changes I've done.

[mfelsche]

@ergl You can generate the new grammar file using your newly compilerd ponyc from your PR and do: ponyc --antlr > pony.g.

[ergl]

Ah, great!

[ergl]

This is ready for review

[SeanTAllen]

I'm holding off on the next release (that contains a "triggers release" fix) as this other large change might be ready soon. My target for the release is no later than this Friday.

[SeanTAllen]

@jemc can you give this a review?

[SeanTAllen]

@ergl are there corresponding tutorial and other changes associated with this that I would need to merge after this is released?

[jemc]

Wow. This was a big initiative. Great work!

[ergl]

@SeanTAllen Yes, the tutorial changes are in pony-tutorial#468

@jemc Thanks! Thank you for also helping me with all LLVM comments and guiding me through the compiler