Gather together usefulness tests

I took most tests that were testing only for match exhaustiveness,
pattern refutability or match arm reachability, and put them in
the same test folder.

src/test/ui/pattern/usefulness/refutable-pattern-errors.rs

@@ -0,0 +1,9 @@
+// ignore-tidy-linelength
+
+fn func((1, (Some(1), 2..=3)): (isize, (Option<isize>, isize))) { }
+//~^ ERROR refutable pattern in function argument: `(_, _)` not covered
+
+fn main() {
+    let (1, (Some(1), 2..=3)) = (1, (None, 2));
+    //~^ ERROR refutable pattern in local binding: `(std::i32::MIN..=0i32, _)` and `(2i32..=std::i32::MAX, _)` not covered
+}