Fix possible_missing_comma false positives

`possible_missing_comma` should only trigger when the binary operator has
unary equivalent. Otherwise, it's not possible to insert a comma without
breaking compilation. The operators identified were `+`, `&`, `*` and `-`.

This fixes the specific examples given in issues #3244 and #3396
but doesn't address the conflict this lint has with the style of starting
a line with a binary operator.

tests/ui/formatting.rs

@@ -112,4 +112,16 @@ fn main() {
         1 + 2, 3 +
         4, 5 + 6,
     ];
+
+    // don't lint for bin op without unary equiv
+    // issue 3244
+    vec![
+        1
+        / 2,
+    ];
+    // issue 3396
+    vec![
+        true
+        | false,
+    ];
 }