Fixed up two issues that were discovered

[SomeRandomiOSDev]

1. When a diagnostic has multiple fix its the annotated string didn't insert newlines between fix-its
2. When a syntax has the same node offset as one of its children, replacing the child with a fix-it would always replace the outermost node

[SomeRandomiOSDev]

Without the fix in DiagnosticsFormatter.swift, this output took the following form:

       ┬──────────────────────────
       ├─ ⚠️ This is the first diagnostic.
       │  ✏️ This is the first fix-it.  │  │  ✏️ This is the second fix-it.  │  ╰─ ℹ️ This is the second diagnostic, it's a note.

[stephencelis]

@SomeRandomiOSDev Thanks for the PR and fixes! Just the one thing about the OptionSet fix, since that's an example that we took from Apple and we may periodically fetch newer versions from them. I don't think it needs to hold up this PR, but if you wanna clean things up let me know!

[stephencelis]

@SomeRandomiOSDev I think @Matejkob also brings up a good point, that this is really an upstream issue that will hopefully be fixed by Apple soon. Because of that, I'm inclined to think we should limit this PR to just fixing the formatting issue to minimize future churn when reintegrating code back from Apple in the future.

[SomeRandomiOSDev]

@SomeRandomiOSDev Thanks for the PR and fixes! Just the one thing about the OptionSet fix, since that's an example that we took from Apple and we may periodically fetch newer versions from them. I don't think it needs to hold up this PR, but if you wanna clean things up let me know!

Makes sense, I'll push a change that moves this fix it to a different macro type to keep the OptionSet macro inline with the one in the swift-syntax repo.

[SomeRandomiOSDev]

@stephencelis @Matejkob I pushed changes that removed the changes to types pulled upstream from swift-syntax and trimmed it down to changes related to this repo only.

[stephencelis]

Thanks!