[fine] Many test improvements, error improvements

- Check for more error conditions
- Move to more definitive error assertions
- Simpler error messages in some cases
- Test more conditions more thoroughly, revisit old tests

fine/tests/expression/errors/duplicate_arguments.fine

@@ -1,5 +1,4 @@
 fun something(x: f64, x: f64) {}
 
-// @ignore
 // @expect-errors:
-// asdfadsf
+// | 1:22: duplicate definition of parameter 'x'