Add a test for function pointer text wrapping.

tests/rust/function_ptr.rs

@@ -0,0 +1,6 @@
+pub type MyCallback = Option<unsafe extern "C" fn(a: usize, b: usize)>;
+
+pub type MyOtherCallback = Option<unsafe extern "C" fn(a: usize, lot: usize, of: usize, args: usize, and_then_some: usize)>;
+
+#[no_mangle]
+pub extern "C" fn my_function(a: MyCallback, b: MyOtherCallback) {}