[EarlyReturn] Deprecate ChangeNestedIfsToEarlyReturnRector

[TomasVotruba]

Inverting nested ifs into early returns flips the logic flow, which makes the code harder to read and understand. Whether it is an improvement depends on the context, so it should not be automated.

 class SomeClass
 {
     public function run()
     {
-        if ($value === 5) {
-            if ($value2 === 10) {
-                return 'yes';
-            }
+        if ($value !== 5) {
+            return 'no';
+        }
+
+        if ($value2 === 10) {
+            return 'yes';
         }

         return 'no';
     }
 }

The 2nd form is not clearly better - the return 'no' is now duplicated and the reader has to mentally re-invert $value !== 5 to get back the original intent.

Follows #8302 and #8303.

ChangeNestedIfsToEarlyReturnRector now implements DeprecatedInterface and throws on use. It was the last rule of the early-return set; the set file and SetList::EARLY_RETURN stay in place (now empty) to avoid a BC break. Also drops the two IfManipulator methods that only this rule used.