Better macros 2.0 formatting

[elenakrittik]

Currently, prettyplease formats them like this, with newlines (seemingly) only being printed when absolutely necessary for line width reasons. This causes frequent merge conflicts where a simple change such as

+    [TypeSpecifier] => { $crate::SyntaxKind::TYPE_SPECIFIER_NODE },

causes a diff like

https://github.com/metallang/metal/pull/145/files#diff-f849ceb9b46f819b3d784180a36767dc7a4aef2d1a4c31e5c8edd0c846e35945L386-R402

Ideally, prettyplease would format multi-arm macros 2.0 just like the normal/"old" macros.