swift

67423687 - [AutoDiff] NFC: `@differentiable` attribute gardening. (#28666)

[AutoDiff] NFC: `@differentiable` attribute gardening. (#28666) - Move `DifferentiableAttr` definition above `DeclAttributes` in include/swift/AST/Attr.h, like other attributes. - Remove unnecessary arguments from `DifferentiableAttr::DifferentiableAttr` and `DifferentiableAttr::setDerivativeGenericSignature`. - Add libSyntax test for `@differentiable` attributes.