Detect missing comma in function declaration

[flashspys]

This PR will make the Parser capable of detect and recover from a missing comma in a function declaration. The motivating example was the following:

func a(foo: Bar foo2: Bar2) {}

 --- Before Diagnostics
 
 1 │ func a(foo: Bar foo2: Bar2) {}
   ∣                 ╰─ unexpected text 'foo2: Bar2' in parameter clause

 
 --- After Diagnostics
 
 1 │ func a(foo: Bar foo2: Bar2) {}
   ∣                 ╰─ expected ',' in function parameter