Quick-Fixes: Support USELESS_CAST diagnostic in "Remove cast" quick-fix

#KT-6422 Fixed

idea/testData/quickfix/expressions/afterRemoveUselessCast.kt

@@ -0,0 +1,4 @@
+// "Remove cast" "true"
+fun foo(a: String) {
+    val b = a
+}

idea/testData/quickfix/expressions/afterRemoveUselessCastUnderSmartCast.kt

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

idea/testData/quickfix/expressions/beforeRemoveUselessCast.kt

@@ -0,0 +1,4 @@
+// "Remove cast" "true"
+fun foo(a: String) {
+    val b = a <caret>as Any
+}

idea/testData/quickfix/expressions/beforeRemoveUselessCastUnderSmartCast.kt

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