Prepare for integer generics with new generic argument node

[Azoy]

With swiftlang/swift-syntax#2859, there will be a new generic argument node that you need to switch over.

[ahoppen]

Ignore the CI failures for now, we need to figure out how to support cross-PR testing, swift-format will get tested as part of your test invocation from swiftlang/swift-syntax#2859. We just need to coordinate merging the PRs because bypassing the CI on this PR requires force-merge capabilities.

But please address the format issues found by https://github.com/swiftlang/swift-format/actions/runs/11524662613/job/32085325124?pr=866

[allevato]

You'll probably also need to make some changes in TokenStreamCreator to make sure that parameter declarations like struct S<let T: Int> (or however it's spelled) get correct whitespace/line-wrapping behavior.

Unfortunately we don't have a good way for the formatter to pass experimental features down to the parser, so that might have to wait. For now, this seems fine (with @ahoppen 's suggested changes) to prevent CI failures from the breaking API change, though.