[FIR] Add RedundantCallOfConversionMethod checker

compiler/fir/analysis-tests/testData/extendedCheckers/RedundantCallOfConversionMethod/nullable2.kt

@@ -0,0 +1,7 @@
+// IS_APPLICABLE: false
+// WITH_RUNTIME
+data class Foo(val name: String)
+
+fun nullable2(foo: Foo?) {
+    val s: String = foo?.name.toString()
+}