Handle function-like attribute macros with generic types in them

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.

Start by reproducing the issue with the #[my_macro(...)] examples, including generic type arguments and a line long enough to require rewriting. Trace rustfmt's handling of function-like attribute macro arguments and verify that the long macro invocation is formatted across multiple lines without changing its contents.