Quick-Fixes: Drop unnecessary parentheses when simplifying cast expressions

#KT-6501 Fixed

idea/testData/quickfix/expressions/afterRemoveUselessCastInParens.kt

@@ -0,0 +1,7 @@
+// "Remove cast" "true"
+fun test(x: Any): Int {
+    if (x is String) {
+        return x.length()
+    }
+    return -1
+}

idea/testData/quickfix/expressions/beforeRemoveUselessCastInParens.kt

@@ -0,0 +1,7 @@
+// "Remove cast" "true"
+fun test(x: Any): Int {
+    if (x is String) {
+        return (x <caret>as String).length()
+    }
+    return -1
+}