Handle function-like attribute macros with generic types in them

[twiby]

When using an attribute macro with a function-like syntax:

#[my_macro(Item1, Item2, Item3)]
fn my_fun() {}

rust fmt can give up if the arguments to the macro are types with generic parameters. If the macro line is too long and should be rewritten in several lines, rust fmt doesn't handle the situation at all:

#[my_macro(Item1<u32>, Item2<u32>, Item3<u32>, Item4<u32>, Item5<u32>, Item6<u32>)]
fn my_fun() {}

Workaround: using an alias for those types to not have to write generic parameters in the macro arguments.