Remove unnecessary filter_var with FILTER_VALIDATE_BOOLEAN option

# Feature Request

When variable is always boolean it is unnecessary to run it trough filter_var with FILTER_VALIDATE_BOOLEAN option.
 
## Diff 

```diff
function test(bool $isTest): bool {
-    if (filter_var($isTest, FILTER_VALIDATE_BOOLEAN)) {
+    if ($isTest) {
        return true;
    }

    return false;
}
```
